April 2011 

NASA/TM–2011-217087 

Remote Measurement of Pollution—A 40-Year 

Langley Retrospective: Part I—Temperature 

and Gaseous Species 

Ellis E. Remsberg 

Langley Research Center, Hampton, Virginia 
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April 2011 

NASA/TM–2011-217087 

Remote Measurement of Pollution—A 40-Year 

Langley Retrospective: Part I—Temperature 

and Gaseous Species 

Ellis E. Remsberg 

Langley Research Center, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 
1 

Contents

Abstract 2 

Background and purposes 3 

Historical context and key players 5 

Objectives and recommendations of the RMOP gas species panel 8 

(a) Objectives and focus 8 

(b) Findings and recommendations 10 

Developments in temperature sounding techniques 13 

Gas species profile or column measurements (1971-1985) 16 

(a) Solar occultation 16 

(b) Limb infrared emission 18 

(c) Partial-column ultraviolet scattering and absorption 21 

(d) Correlation radiometry and active sensing for tropospheric species 23 

Changing priorities and technology advancements (1986-1996) 25 

(a) Science and politics 25 

(b) The “Antarctic ozone hole” and trends in global ozone 27 

An Earth Observing System (EOS) plus international contributions (1997-2010) 33 

Joint Polar Satellite System (JPSS) and future sensing prospects 37 

Summary 41 

Acknowledgements 41 

Appendix A—Acronyms 42 

References 50
2 

Abstract

The National Aeronautics and Space Administration (NASA) phased down its Apollo Moon 

Program after 1970 in favor of a partly reusable Space Shuttle vehicle that could be used to 

construct and supply a manned, Earth-orbiting Space Station. Applications programs were 

emphasized in response to the growing public concern about Earth’s finite natural resources and 

the degradation of its environment. Shortly thereafter, a workshop was convened in Norfolk, 

Virginia, on Remote Measurement of Pollution (or RMOP), and its findings are in a NASA 

Special Publication (NASA SP-285). The three primary workshop panels and their chairmen 

were focused on trace gas species (Will Kellogg), atmospheric particulates or aerosols (Verner 

Suomi), and water pollution (Gifford Ewing). Many of the workshop participants were 

specialists in the techniques that might be employed for the regional to global-scale, remote 

measurements from an Earth-orbiting satellite. The findings and recommendations of the RMOP 

Report represent the genesis of and a blueprint for the satellite, atmospheric sensing programs 

within NASA for nearly two decades. This paper is a brief, 40-year retrospective of those 

instrument developments that were an outgrowth of the RMOP activity. Its focus is on satellite 

measurement capabilities for temperature and gaseous species that were demonstrated by 

atmospheric technologists at the Langley Research Center. Limb absorption by solar 

occultation, limb infrared radiometry, and gas filter correlation radiometry techniques provided 

significant science data, so they are emphasized in this review. 
3 

1 Background and purposes 

The Apollo Moon Program of NASA, though highly successful, would be ending in the early 

1970s. Further production of the Saturn V, heavy-lift launch vehicle was cancelled in favor of 

developing a partially reusable, Space Shuttle vehicle that could be used to construct and then 

resupply a manned, Earth-orbiting observatory [Hansen, 1995]. NASA began to emphasize its 

Space Applications programs. There was growing public concern that natural resources were 

finite and that the Earth environment was being degraded. The Clean Air Act (CAA) was signed 

into law in 1970, and it meant a major shift in the role of the federal government in controlling 

air pollution. That legislation authorized the development of comprehensive federal and state 

regulations to limit emissions from both stationary (industrial) sources and mobile sources. 

Then, on May 2, 1971, the U.S. Environmental Protection Agency (EPA) was created to 

implement the various requirements of the CAA. The following year Congress passed the Clean 

Water Act (CWA) designed to limit pollutant discharges from point sources, such as industrial 

and municipal facilities.

Significant concerns were also raised in 1970 about the prospect of deleterious effects on life of 

the excess ultraviolet (uv) radiation from a chemical loss of ozone (O3), as a result of the spread 

of water vapor (H2O) from the exhaust plumes of a commercial fleet of supersonic transport 

(SST) aircraft flying in the lower stratosphere. Funding for the continued development of a 

Boeing SST prototype was halted by the U.S. Congress in March 1971, but primarily to await an 

interim decision on landing rights in the U.S. for the Anglo-French Concorde aircraft [Wayne, 

1991]. Shortly thereafter, studies were reported on the likely catalytic loss of O3 due to the 

nitric oxide (or NO) emitted by their engines. Several federal agencies, including NASA, were

eventually assigned a Congressionally-mandated responsibility for researching and monitoring 

the stratospheric ozone layer under the CAA amendments of 1977. Laboratory reaction rate 

measurements and more accurate and extensive atmospheric observations that they funded would 

be key to understanding of the relative roles of transport and of the hydrogen and nitrogen oxide 

chemical families (HOx and NOx) on the ozone layer. 

In the international arena two separate study groups met to assess the potential human impact on 

the global environment [SCEP, 1970; SMIC, 1971]. Their findings included recommendations 

for global observations and for further research to distinguish between the effects of man-made 

versus natural pollutants. In particular, they expressed a need for the identification and/or 

monitoring of specific environmental contaminants, including trace gas species, particles, and 

water pollutants. Environmental issues of the time included the regional-scale transport of 

pollution, acid rain, and the degradation of ecosystems and coastal estuaries. Thus, at a time 

when NASA was in transition it was natural to ask whether a segment of its technology 

workforce could demonstrate the use of atmospheric remote sensing techniques for making 

measurements of the global environment. NASA embarked on the development of satellite 

techniques for an improved understanding of the distributions, sources, and sinks of pollutants. 

The Agency had already demonstrated the promise of global weather observations and of 
4 

communications from Earth-orbiting satellites. NASA had also been conducting systematic, 

scientific studies of the atmospheres of the other planets [Conway, 2008]. 

Morris Tepper, Director of Meteorology Programs, and Jules Lehmann, Manager of Advanced 

Instrumentation and Sensor Engineering Programs, both of NASA Headquarters, directed that 

Langley Research Center (LaRC) convene a Working Group on the topic of the Remote 

Measurement of Pollution (RMOP). They, along with Henry Reichle, Jr., and Wendell Ayers of 

Langley, quickly assembled a panel of experts and were the hosts for a Workshop on the RMOP 

in Norfolk, Virginia, August 16-20, 1971. The three primary RMOP panels and their chairmen 

were focused on gaseous air pollution (Will Kellogg), particle air pollution (Verner Suomi), and 

water pollution (Gifford Ewing). Two additional panels reviewed and reported on the principles 

of remote sensing and the associated instrument techniques. Findings of the RMOP panels can 

be found in NASA SP-285 [1971], and NASA went on to redefine the final satellite in its 

Nimbus series (Nimbus 7) as a “pollution patrol” satellite [Conway, 2008]. Later, several of its 

successful sensor prototypes were refined and became operational on NOAA satellites, as 

envisioned. Of course, the international community contributed to the development and 

deployment of their own satellite-borne sensors. The historical evidence indicates that the 

findings of the SCEP Report and the RMOP Workshop Report represent the genesis of and 

blueprint for the satellite Earth-sensing programs within NASA for the following two decades. 

This report (or Part I) is a 40-year retrospective of the instrument developments and 

demonstrated remote measurement capabilities for temperature and gaseous species from Earth 

orbit that were an outgrowth of RMOP. A second report (or Part II) is planned, and it will be 

devoted to the remote measurement of clouds and particulate air pollution. Although the focus 

of Part I is on the research activities within LaRC, they are described within the context of the 

ongoing work at Jet Propulsion Laboratory (JPL), NASA Goddard and Ames, the National 

Oceanic and Atmospheric Administration (NOAA), and the academic and international 

communities. Section 2 reviews the early work on atmospheric measurements at Langley and 

notes several of the key players for the RMOP Workshop. Section 3 summarizes the objectives 

and recommendations of the Gas Species Panel in the context of what was known in 1971. The 

Panel focused on the inference of gas species profiles derived from the spectral signatures of 

their atmospheric transmission or infrared radiance. Because a good knowledge of the associated 

atmospheric density or temperature is also needed, Section 4 is a short summary of the progress 

since 1971 for achieving those accurate and co-located profiles. Section 5 is a more extensive 

account of the primary measurement techniques that were selected for obtaining gas species 

profiles from Earth orbiting satellites and Shuttle-launches from 1971-1985. Section 6 

comments on the changing science priorities and the relevant technologies at Langley prior to the 

Earth Observing System (EOS) era. Section 7 discusses the complement of sensors for EOS and 

their capabilities. Section 8 looks briefly to the Joint Polar Satellite System (JPSS) and then to

several proposed sensor applications from Langley for the coming decade. Finally, Section 9 

reiterates the findings and concludes that many of the objectives of the original Gas Species 

Panel were met. Key papers are cited throughout to support the conclusions in this retrospective.
5 

2 Historical context and key players 

Langley Research Center has traditionally been focused on developing and applying 

measurement technologies for studies of flight models in wind tunnels or of test aircraft in the 

atmosphere. One might wonder why Langley Research Center was chosen to organize the 

RMOP activity. As the primary field center for NASA’s predecessor, the National Advisory 

Committee for Aeronautics (NACA), Langley researchers contracted with the Weather Bureau 

and the Navy Department for the development of reference atmosphere models that represented 

the range of conditions to be expected for aircraft flight below about 20 km [Gregg, 1923; Diehl, 

1926]. Later, the NACA extended its models to 120 km based on rocket soundings or from 

indirect measurements, such as meteor trails and ionospheric fade-out phenomena [Warfield, 

1947; Craig, 1965]. Langley was also well-known for its expertise in the development of both in 

situ and remote optical measurement probes [Crumbly, 1970]. In the 1950s and 1960s Langley 

successfully conducted and/or managed the Echo satellite Project for passive space 

communications, the solid-propellant Scout launch-rocket program, the Apollo capsule re-entry 

Project FIRE, and the Lunar Orbital Program for selecting appropriate sites for Apollo landings 

on the Moon [Hansen, 1995]. Langley researchers developed and launched inflatable air density 

satellites to characterize the state of the thermosphere for estimating orbital lifetimes [e.g., 

Keating and Prior, 1967]. Many others were involved with the design and testing of structures 

and materials for spacecraft and with the evaluation of horizon sensing methods for navigation, 

guidance, control, and re-entry in support of the Mercury, Gemini, and Apollo programs. 

Figure 1 is a time line that begins (at left) with the aeronautics-related activities at Langley prior 

to 1971. The next decade might be considered a time of “exploring new techniques for making 

measurements of Earth’s atmosphere” within NASA. It wasn’t long though before the concerns 

about the possible loss of stratospheric ozone prompted demonstrations of measurement methods 

for actually obtaining accurate temperature and gas species data at those altitudes. Langley in 

that intervening 40-yr period (at right) became focused on three principal satellite remote sensing 

methods—limb absorption via solar occultation, limb infrared emission, and gas filter correlation 

radiometry. The primary Langley instrument scientists responsible for applying those methods 

were M. Patrick McCormick, James M. Russell, III, and Henry G. Reichle, Jr., respectively. 

Presently, McCormick and Russell are the Co-directors of the Center for Atmospheric Sciences 

at Hampton University. Further satellite remote sensing initiatives from LaRC for the decade 

following 2010 are then noted at the bottom of Figure 1, and they will be discussed briefly in 

Section 8. 

 

Several persons, besides Tepper and Lehmann, were important to the success of the RMOP 

Workshop. Edgar Cortright, a pragmatic environmentalist, was Langley Director from 1968-

1975, and he led the program that sent the Viking 1 and 2 combined orbiter/lander spacecraft to 

Mars in 1975-76. While at NACA and then NASA Headquarters in the late 50s and early 60s, 

Cortright was involved with the formulation of technology for the Agency’s meteorological 

satellites—Television Infrared Observation Satellite (TIROS) and Advanced Technology 

Satellite (ATS). In 1959 he suggested the name for the follow-on research satellite series, 
6 

Nimbus. The Nimbus Project was managed initially by William Stroud of NASA Goddard and 

had a rocky beginning, but following the launch of Nimbus 1 in 1964 it eventually became the 

demonstration program for the satellite Earth-imaging and sounding instruments and for 

meteorological science within NASA [Conway, 2008]. At Langley Cortright supported the 

RMOP Workshop and formed the Flight Instruments Division (FID) and the Environmental and 

Space Sciences Division (ESSD), wherein some of the RMOP-recommended, sensor 

development and demonstration would occur. In 1972 NASA Headquarters formed an Office of 

Applications (OA), led by Chuck Mathews, a Langley veteran [Conway, 2008]. Specific NASA 

Earth-observing satellites and research instruments would be funded by OA and demonstrated 

via flight tests under contracts managed by Goddard Space Flight Center, Jet Propulsion 

Laboratory, and the Ames and Langley Research Centers. Initial support for instrument 

development was obtained through peer-reviewed proposals to the new Advanced Applications 

Flight Experiments (AAFE) Program, managed by Jules Lehmann of NASA Headquarters.

The NASA Environmental Quality Program Office (EQPO) was formed at Langley in 1972 and 

put under the direction of J. D. Lawrence, Jr., who had been Chief Scientist of ESSD. In 1976 

Donald Hearth succeeded Cortright as Langley Director and formed the Atmospheric 

Environmental Sciences Division (AESD). Geographically, Langley is relatively close to 

Research Triangle Park in North Carolina, the location of the primary field center of the newlyformed EPA. This proximity to each other led to their joint conduct of several NASA/EPA field 

measurement campaigns in the early 1980s on studies of regional ozone and aerosol pollution 

events using a combination of ground-based, airborne, and satellite observing techniques 

[Fishman et al., 1985]. 

AESD was renamed the Atmospheric Science Division (ASD) in 1982, when emphasis on 

environmental issues was reduced within the Reagan administration and for NASA. Lawrence

remained as the Head of AESD and then ASD for 18 years. The leadership of ASD continued 

thereafter under Robert Seals, Jerry Newsom, William Smith, Sr., and Leonard McMaster. ASD 

expanded its capabilities and is known presently as the Science Directorate (SD); it is currently 

led by Lelia Vann. Stephen Sandford leads Langley’s Systems Engineering Directorate and

contributes to NASA’s Earth Science Programs by managing the development of advanced 

concepts and technologies and the demonstration of the measurement techniques both in the 

laboratory and from flight platforms. Somewhat necessarily, this retrospective is focused on the 

development and heritage of the satellite remote sensing activities at NASA Langley, where the 

author was a researcher for FID/ESSD/AESD/ASD/SD during his contract and civil service 

career from 1971-2010.
7 

RMOP 

Workshop

1971

•Create model atmospheres, 

ground to thermosphere.

•Passive sensing studies of 

Earth’s CO2 horizon for 

spacecraft attitude and 

reentry.

•Laser sensing of fluid flow in 

wind tunnels and turbulence 

in the atmosphere

•Satellite infrared limb emission 

sensors.

•Satellite measurements by 

solar occultation (SO).

•Satellite Gas Filter Correlation 

Radiometry (GFCR) techniques.

1940’s Present

•Hyper-spectral imaging of troposphere

•Limb scattering for lower stratospheric ozone

•SO via SAGE III from Space Station

•Tunable lasers for partial column CO2

•Geostationary GFCR measurements for CO.

Aeronautics Focus 

Remote Sensing Application

Sensors for the Next Decade

Figure 1. Time line of the application of techniques by NASA Langley for making 

measurements of the atmosphere. 
8 

3 Objectives and recommendations of the RMOP gas species panel

(a) Objectives and focus 

The primary role of the Space Applications programs of NASA is the development of satellite 

techniques for monitoring the effect of human activities on the environment. The RMOP 

participants made evaluations of the role of remote sensing in identifying specific pollutants and 

in measuring them with certain accuracies. Members of the Gas Species Air Pollution Panel are 

listed in Table 1. William Kellogg of NCAR was Chair of the Panel, and he was assisted by 

James Russell III and Gary Grew of Langley. Panel member, William Matthews of MIT, was an 

editor of the SCEP and SMIC Reports and had worked with Kellogg on those earlier study 

initiatives. The RMOP Panel reviewed the information about pollutants, e.g., their physics, 

chemistry, biological effects, distributions, etc. Member names in boldface print can be directly 

associated with satellite sensor concepts following RMOP. Further, the Panel decided at the 

outset that they would consider only those pollutants and trace gases that are important on a 

global or regional scale, i.e., scales most amenable to satellite sensing or areas of one million 

square kilometers or more. 

There had already been efforts to study the stratosphere in the 1950s and early 60s related mostly 

to an understanding of the transport and distribution of radioactive debris from high-altitude 

atomic tests and the deposition or fate of the debris once it entered the troposphere. It was 

known that ozone is an effective tracer of stratospheric air entering the upper troposphere 

[Reiter, 1971]. There was also interest in determining the formation, transport, and decay of 

volcanic stratospheric aerosol layers, as they are useful analogs for the transport of radioactive 

bomb debris. The role of sulfur gases for the formation of both the stratospheric background and 

volcanic aerosol layers was a topic of research at that time. Will Kellogg was active in all these

research areas throughout his career [e.g., Kellogg et al., 1957; Kellogg et al., 1972]. 

The release of a large quantity of H2O from a fleet of supersonic transport (SST) aircraft had 

been reported as likely to cause a small, but measureable loss of column ozone [Harrison, 1970]. 

In 1971 a new issue arose about the chemical loss of ozone due to the molecules of NO 

originating with the high-altitude atomic tests of the early 1960s [Foley and Ruderman, 1973], 

and which would also be released by a fleet of SSTs [Johnston, 1971; Crutzen, 1970]. Concerns 

about the effects of both H2O and NO on O3 led to the rather comprehensive, scientific Climatic 

Impact Assessment Program (CIAP) conducted by the U.S. Department of Transportation (DOT) 

from 1971-74. It is important for the reader to recall that the scientific understanding of the 

chemical effects of H2O and NOx on ozone were quite uncertain at that time [e.g., Ellsaesser, 

1982]. Further, although it was known that the concentrations of the manmade, but relatively 

inert, chlorofluorocarbon compounds (CFCs) were increasing in the troposphere, their eventual 

photolysis in the upper stratosphere and the involvement of their dissociation products in the 

destruction of ozone was not fully realized at the time of the RMOP Report. 
9 

Satellite measurement capabilities for obtaining vertical profiles of O3 had been demonstrated for 

the upper stratosphere by 1971 from Orbital Astronomical Observatory (OAO) using stellar 

absorption and from Nimbus 4 by solar backscatter ultraviolet (BUV) absorption. Water vapor, 

nitrogen dioxide (NO2), sulfur dioxide (SO2), and nitric acid (HNO3) had also been measured 

using ground-based, balloon-borne, or rocket-borne remote sensors by that time, but not yet with 

the accuracies that were needed to resolve questions about their interactions with ozone. The 

Panel wanted to achieve total O3 and stratospheric O3 profiles to 1% and 10% accuracies, 

respectively. Further, they desired measurement accuracies for H2O (20%), CH4 (0.2 ppm), N2O 

(50 ppb), NO, NO2, and CO (10 ppb), HNO3 (1 ppb), and SO2 (0.5 ppb) in the stratosphere, and 

they wanted to achieve them with vertical profile resolutions of a few kilometers. In fact, an 

underlying theme for all the sensors was how to obtain accurate species profiles with adequate 

spatial resolutions. 

In the early 1960s concerns had also arisen about the effects of urban-scale pollution on regional 

air quality, due to earlier decisions to construct taller power plant stacks for the release of their 

point-source pollutants to somewhat higher altitudes within the atmospheric boundary layer. The 

members of the Gas Species Panel recognized that instead of the surface concentrations it may 

only be possible to measure the total burden of a gas above the surface because of the inherent 

limitations of the remote sensing concepts of that time. Total burden measurements of certain 

gases were being made already via ground-based, solar absorption techniques. Still, the Panel

felt that knowing the horizontal spatial distributions of those gas burdens would be extremely 

helpful in following the transport of species from source regions and perhaps of their conversion 

to secondary pollutants. Such information was considered complementary with that being 

obtained from the ground-based instruments. The Panel wanted to achieve tropospheric 

measurement accuracies for CO2 and CH4 of 0.5 ppm and for O3, CO, SO2, and NH3 of 10 ppb. 

The Panel members judged that the following species could also have an impact on the quality of 

the global environment. For instance, the concentration of CO2 had been increasing since the 

industrial revolution because of the burning of fossil fuels. CO2 traps part of the outgoing 

infrared radiation emitted by the Earth’s surface and contributes to an increase in the average 

surface temperature. NOAA’s new program of Geophysical Monitoring for Climatic Change 

(GMCC) was headed by Panel member, Donald Pack, and was focused on global trends in CO2

and possibly other source gases. Nadir-viewing, satellite remote sensors ought to prove useful in 

tracking the movements of CO2 from its sources to its sinks. Carbon monoxide (CO), SO2, NOx, 

and halogen gases are other pollutants from the combustion of fossil fuels or products of certain 

agricultural and industrial activities. Atmospheric methane (CH4), nitrous oxide (N2O), 

hydrogen sulfide (H2S), SO2, and certain hydrocarbons have large, natural source components. 

Panel member, Allen Lefohn of EPA, was an expert on the effects of ozone and peroxyacetyl 

nitrates (PAN), secondary pollutants in the troposphere arising from photochemical reactions 

involving nitrogen oxides and hydrocarbons. Ozone itself is harmful to forest and agricultural 

plants. Panel member, John Ludwig of EPA, was a proponent of applying sensor technology to 

the study of emissions from pollution sources and the transport of pollution regionally and 
10 

perhaps globally [e.g., Ludwig, 1971]. Such regional to global scale concerns had also been

outlined in a related National Academy of Sciences Panel Report [NAS, 1969]. 

(b) Findings and recommendations 

The Panel reported that tropospheric temperature profiling was successful in 1969 from Nimbus 

3 with its satellite, multichannel infrared spectrometer (SIRS) instrument that included a 

reference blackbody for in-flight calibration [Wark and Hilleary, 1969]. Rudy Hanel and 

colleagues at NASA Goddard employed Michelson interferometry for their infrared 

interferometer spectrometer (IRIS) to identify species in the atmospheres of both Earth and Mars. 

IRIS operated successfully from Nimbus 3 and 4, revealing spectral features from tropospheric 

H2O and lower stratospheric O3, in addition to CO2 [Hanel and Conrath, 1969]. 

Stratospheric temperature profiles were being retrieved reliably by John Houghton and 

colleagues of the University of Oxford from nadir radiances measured with a CO2 gas-cell, 

correlation approach, i.e., their selective chopper radiometer (SCR) instrument on Nimbus 4 

[Houghton et al., 1984]. Donald Heath of NASA Goddard was also obtaining stratospheric 

partial column ozone measurements using the BUV approach from Nimbus 4. Solar, limb 

absorption was shown to be useful for the measurement of atmospheric extinction and of O3 by 

Panel Member, Ted Pepin, of the University of Wyoming. Balloon-borne, infrared limb 

emission techniques were being evaluated for the measurement of stratospheric trace gas species 

by David Murcray of the University of Denver, and an extension of those techniques had been 

proposed by Panel members, John Gille and James Russell, for the measurement of temperature, 

O3, and H2O on Nimbus F (designated Nimbus 6 after launch). 

The Panel members developed a consensus of satellite remote sensing possibilities for the 

various measurements. Factors that they considered were the spectral signatures of the

pollutants, difficulties with data interpretation in the ultraviolet, visible, infrared or microwave 

regions, and the availability and sensitivity of instruments and detectors in the different spectral 

ranges. A comprehensive feasibility study had been underway already, led by Panel member, 

Claus Ludwig [Ludwig et al., 1974]. Because many in the Panel also had experience with 

developing and applying one or more of the specific minor or trace gas measurement techniques, 

they were able to evaluate the sensor capabilities of that time. They classified them according to 

atmospheric limb or vertical profiling techniques, by uv backscatter, thermal emission, or 

absorption. Both solar and stellar uv measurements of O3 had been demonstrated from balloon, 

rocket, and early satellite platforms. Balloon-borne, limb-infrared measurements showed 

promise for inferring profile measurements of minor and trace gases in the stratosphere, once the 

effects of temperature are included for the calculation of their forward radiances. They reported 

that solar absorption measurements offered good specificity and accuracy for many gases, 

although often only as column burdens for the tropospheric pollutants. Correlation spectrometry 

could be applied to the measurement of SO2 in the ultraviolet (uv) and of NO2 at visible 

wavelengths. Both grating and correlation spectrometers were being employed for the 

detection and tracking of atmospheric species by Panel members, Barney Farmer of JPL and 
11 

Tony Barringer of Environment Measurements Inc., respectively. Panel member, Philip Hanst of 

EPA, was using tunable gas lasers for the detection of pollutants from ground-based sources. On 

the other hand, the RMOP Panel judged that the prospects were still unclear for making useful 

atmospheric pollution measurements via a passive microwave sounder from a satellite.

The Gaseous Species Panel made the following, rather broad recommendations in their report. 

Distributions of the stratospheric gases that play a part in determining the photochemistry of 

ozone and of the atmospheric radiative equilibrium state should be measured concurrently on a 

global basis from satellites. Primary constituents of interest were H2O, NO, NO2, HNO3, CH4, 

and O3 itself. Panel members did not establish that all these gases could be measured with 

current techniques; therefore they recommended that a development program be undertaken to 

determine the feasibility of measuring the species distributions to their required accuracies. 

Trade-offs are involved for making accurate measurements of radiance or transmission profiles 

and for retrievals of the information content and vertical resolution of their temperature and gas 

species profiles, as reviewed subsequently in Houghton et al. [1984]. Remote measurement 

techniques from satellites should be exploited to measure regional and global distributions of 

gaseous pollutants in the troposphere, as well—the objective being to establish sources and sinks 

and to assess the roles of these gases in the environment. Trace gases that might be measureable

in this manner and to the required accuracy were CO, SO2, NO2, NO, and possibly CO2. Studies 

would need to be initiated to relate the vertical burdens and surface concentrations of the trace 

gases, and the findings should be used in the planning of complementary programs to measure 

pollutants from both the ground and Space.

The Panel recommended that remote measurement techniques be developed and applied to 

determine vertical concentration profiles of pollutants, and that their measurements should be 

used to improve transport models and to study the space and time variations of species. They 

noted that laboratory studies were needed to obtain more accurate values of the basic absorption 

properties of the pollutant molecules, i.e., line strengths, half-widths, and positions in the 

infrared and microwave regions of the electromagnetic spectrum. Research programs would 

need to be focused on advancing the state-of-the-art beyond the current instrumentation 

capabilities, with particular emphasis on those systems that appear to be potentially feasible from 

satellite altitudes. The Panel relied somewhat on performance assessments that were being 

conducted for the different types of instruments: radiometers, grating spectrometers, 

interferometers, optical correlation spectrometers, and laser probes (e.g., see Ludwig et al. [1974] 

and references therein). They recommended that both microwave techniques and active systems 

employing lasers be explored more fully. Panel members, Jacob Becher of Old Dominion 

University and Gary Grew of Langley, provided insight on the possible effects of space radiation 

on likely optical measurement systems and detectors. In addition to satellites, the Panel 

members emphasized the need to use aircraft and balloon platforms, for studying regional 

pollution problems and for evaluating the new techniques for their eventual use from Space. It is

also noteworthy that NAS [1969] recommended that the National Center for Atmospheric 

Research (NCAR) and NASA coordinate their programs and make better use of the NASA 
12 

Wallops Island facility in Virginia, a unique sounding rocket and radar tracking station for the 

testing of proposed, remote atmospheric probing methods. 

Table 1. RMOP members of the Gas Species Panel and their affiliations in 1971 

William Kellogg, NCAR, Panel Chair

Tony Barringer, Environmental Measurements, Inc. 

Jacob Becher, Old Dominion Univ. 

C. Barney Farmer, JPL 

John Gille, Florida State Univ. 

Gary Grew, NASA Langley

Philip Hanst, Div. of Chemistry and Physics, EPA 

Allen Lefohn, Div. of Chemistry and Physics, EPA

Claus Ludwig, General Dynamics Corp.

John Ludwig, Office of Air Programs, EPA 

William Matthews, MIT

Donald Pack, Air Resources Lab, NOAA 

Ted Pepin, Univ. of Wyoming 

James Russell, III, NASA Langley

Harold Yates, NESS, NOAA
13 

4 Developments in temperature sounding techniques

The major objective of atmospheric measurements from satellites in the 1960s was to obtain 

global data on temperature and water vapor and on the presence of clouds for the purpose of 

improving weather forecasts. NASA Goddard led the technology development for the TIROS 

and Nimbus meteorology satellite programs, but in coordination with the needs of NOAA and 

Department of Defense (DOD). Houghton and Smith [1970] provide an excellent tutorial on the 

difficulties of developing a remote sensor having both high spectral resolution and significant 

energy-gathering power. The Selective Chopper Radiometer (SCR) on Nimbus 4 is their initial 

solution for achieving temperature profiles in the stratosphere from radiance measurements in the 

nadir direction. Their retrieved temperatures are of relatively low vertical resolution or no better 

than an atmospheric scale height. Panel member, Harold Yates, of the National Environmental 

Satellite Service (NESS) of NOAA reported on methods for the retrieval of temperature from 

CO2 radiances, as well as retrievals of H2O and O3 profiles after applying those temperatures in 

their analyses of the infrared emissions from those two gases. That approach had been 

demonstrated several years earlier with the nadir-viewing experiments, Infrared Interferometer 

Spectrometer (IRIS) and Satellite Infrared Spectrometer (SIRS) on Nimbus 3, and from the 

Temperature Humidity Infrared Radiometer (THIR), IRIS, and SCR on Nimbus 4. In addition, 

atmospheric O3 profiles of moderate vertical resolution were also obtained for the middle and 

upper stratosphere using the nadir-viewing BUV instrument on Nimbus 4.

Ground-based atmospheric measurements of the 1960s indicated that one could also expect to

obtain temperature and water vapor profiles from a satellite instrument operating at the 

microwave emission frequencies of O2 and H2O, respectively. A distinct advantage of the 

microwave measurement is that its signals are unaffected by clouds. One such instrument, the 

Nimbus E Microwave Spectrometer (NEMS), had already been developed for flight and was 

launched on Nimbus 5 in December 1972. An Infrared Temperature Profile Radiometer (ITPR), 

the Surface Composition Mapping Radiometer (SCMR), an Electronic Scanning Microwave 

Radiometer (ESMR) instrument, and an improved version of the Nimbus 4 SCR instrument also 

operated successfully from Nimbus 5. The SCMR and ESMR instruments were precursors to the 

more sophisticated imagers that would be deployed by Goddard and JPL from Earth observation 

satellites in the following decades. Imagery from SCMR also provided information about the 

transport of atmospheric dust and industrial pollution. Staelin et al. [1977] of MIT and personnel 

at JPL were successful in demonstrating retrievals of tropospheric and lower stratospheric 

temperature profiles with their Scanning Microwave Spectrometer (SCAMS) instrument on 

Nimbus 6 in 1975. Its successor, the Microwave Sounding Unit (MSU) instrument, was selected 

by NOAA for its series of TIROS operational vertical sounders (TOVS) beginning in 1979. 

A Pressure Modulator Radiometer (PMR) instrument also obtained measurements of atmosphere 

radiance from Nimbus 6 [Curtis et al., 1974; Houghton et al., 1984; Lawrence and Randel, 

1996]. The PMR instrument includes in its optical system gas cells containing CO2 gas whose 

pressures are modulated at selected frequencies. This PMR approach is analogous to that of the 

SCR but has the distinct advantage that the transmission through the gas cell and the radiation 
14 

incident at its detector is modulated only at the frequencies within the absorption lines of the CO2 

gas itself. In effect, the CO2 in the cell acts as a spectrally selective filter for emissions from the 

CO2 in the atmosphere. By this method one can essentially eliminate the effects of interfering 

emissions in the same wavelength band due to other atmospheric gases, and this approach was 

used later to infer the profiles of several trace gas species in the stratosphere, as well (see Section 

5). The PMR instrument on Nimbus 6 carried two cells of CO2, but with differing CO2 amounts 

and pressure modulation ranges in order to be sensitive to radiance levels from the stratosphere 

and mesosphere. In this case because the atmospheric mixing ratio of CO2 is uniform and 

known, one can infer the atmospheric temperature value that accounts for the radiance at the 

detector of each cell. Still, the final temperature profile obtained from the combined 

measurements from the two cells for a given sounding has an effective vertical resolution that is 

not much better than that from the SCR. However, on Nimbus 7 they used the PMR method to 

observe the atmosphere in the limb mode with the follow-on Stratospheric and Mesospheric 

Sounder (SAMS) experiment. The longer path of the limb-viewing geometry for the SAMS 

measurements and their narrower atmospheric weighting functions provided temperature profiles 

throughout the middle atmosphere from late 1978 to 1983 and with an effective vertical 

resolution of about 8 km [Barnett and Corney, 1984]. 

The PMR measurement of CO2 radiance and the retrieval of atmospheric temperature from 

Nimbus 6 was the demonstrated precursor to the Stratospheric Sounding Unit (SSU) instrument 

for TOVS. The TOVS series of NOAA operational satellites also included a high resolution 

infrared radiation sounder (HIRS), whose capabilities were demonstrated initially on Nimbus 6 

[Feddes and Liou, 1977]. HIRS was a 17-channel radiometer and its measurements together 

with those from the MSU provided the first opportunity for obtaining satellite temperature 

retrievals in cloudy atmospheres. Accurate retrievals of the temperature profile are critical for 

obtaining even low vertical resolution water vapor profiles from infrared channel radiances. 

Thus, NOAA combined the three instruments (HIRS, MSU, and SSU) for obtaining temperature 

profiles throughout the stratosphere and troposphere, even in the presence of clouds. 

Unfortunately, the successful, joint NOAA/NASA operational satellite improvement programs 

were ended in 1982, when the U.S. government became less interested in sensor technology 

development for routine Earth observations [Conway, 2008]. It would be two decades later in 

2002 when the Advanced TOVS (or ATOVS) sensor concept was launched by NASA on its 

EOS Aqua satellite. ATOVS consists of an Advanced Microwave Sounding Unit (AMSU) plus 

the Atmospheric Infrared Sounder (AIRS) of the JPL for temperature soundings [Chahine et al., 

2006]. AIRS has nearly 2400 infrared channels and thereby provides improved S/N for the 

retrieval of both the tropospheric temperature and moisture profiles. AMSU is an improvement 

over the MSU, although with many fewer channels in the vertical than AIRS. Still, the 

microwave measurements are insensitive to the clouds. 
15 

In the early 1970s William Smith, Sr., of NOAA (and then of NASA Langley from 1997-2004) 

knew that the tropospheric infrared sounders must provide even greater vertical resolution, in 

order for their temperature and moisture profiles to gain further improvements in the weather 

forecasts. He proposed a High-resolution Interferometer Sounder (HIS) concept [Smith et al., 

1979] based on the original IRIS instrument of Rudy Hanel. The development of HIS was aided 

by the experience gained by Harold Goldstein of General Electric with his Correlation 

Interferometer for the Measurement of Atmospheric Trace Species (CIMATS) instrument, a 

measurement concept supported at Langley through the AAFE Program. Smith built a prototype 

version of the HIS instrument and successfully tested it in a number of airborne campaigns. 

However, the full satellite realization of the original HIS concept was not achieved until some 25 

years later upon the launch in 2006 of the European polar orbiting satellite MetOp-A and the 

Infrared Atmospheric Sounding Interferometer (IASI) with its more than 8400 infrared channels. 

Combinations of AMSU and AIRS on EOS Aqua and of AMSU, IASI, and the Microwave 

Humidity Sounder (MHS) on MetOp are leading to significant improvements in the skill of 

medium range weather forecasts at the present time [Smith, 2010]. Most recently, the combined 

goals of improved accuracy and much higher vertical resolution have been demonstrated for 

temperature and tropospheric water vapor from a set of six microsatellites using the Global 

Positioning System (GPS) radio occultation (RO) receivers and limb sounding techniques of the 

JPL [Anthes et al., 2008]. Those RO soundings are resolving the vertical temperature variations 

of the tropopause region and of the planetary boundary layer for the first time from satellites. 

Nevertheless, even in 1971 the RMOP Panel members were aware that in order to obtain 

meaningful ozone data from its satellite-measured, infrared radiance profiles, it is critically 

important to also have co-located temperature profiles and with a vertical resolution that is very 

similar to that desired for the ozone. This capability is necessary in order to characterize the 

Planck function properly in the forward radiance model of the measured ozone radiances. 

Compatibility between the temperature and ozone is also important for a proper interpretation of 

the effects of both chemistry and transport on ozone in the stratosphere. Accurate pointing 

knowledge for the associated, co-located temperature and/or atmospheric density profiles is also

required for the registration of the satellite, limb radiance or limb absorption measurements, as a 

function of pressure or altitude. This capability of obtaining high-quality, temperature, density, 

and radiance profiles was a significant factor for the design of the satellite instruments for the 

“pollution patrol” satellite, Nimbus 7, and thereafter, as noted in the next section.
16 

5 Gas species profile or column measurements (1971-1985) 

The Nimbus satellites operated in polar orbit, and they were focused mostly on the 

demonstration of sensor concepts. Observations from Nimbus 4 in 1970 provided measurements 

of good precision and near-global scale temperature and ozone distributions that were relatively 

accurate. However, it was clear to the RMOP Panel members that in order to resolve questions 

about the sources and fate of chemical pollutants in the stratosphere or the troposphere, one must 

obtain more accurate, global-scale data on the relevant trace gas species and with sufficient 

vertical resolution. Each sensor technique must be able to provide its retrieved species with 

acceptably small uncertainties. Tepper and J. D. Lawrence recognized in 1971 that improving 

the standing of the Space and Earth Sciences in the larger scientific community required renewed 

attention to the fundamentals of scientific practice, and operationally this meant engineering the 

instruments for credibility [Conway, 2008]. The capability for frequent, in-flight calibrations 

had to be developed for the instruments, and comparisons with known, co-located measurements 

would need to be carried out, especially during the test flights of a given instrument. Ultimately, 

the selection of an instrument for a spaceflight opportunity would be based on its scientific goals 

and on the performance of its test remote sensor. 

Langley atmospheric science and engineering researchers began to play to their strengths in the 

1970s and 1980s—solar occultation, infrared limb emission, radiation budget measurements, and 

lidar. It must be noted though that in the early to mid 1970s Langley technologists were also 

applying cameras, imagers, and laser fluorescence techniques to quantify the presence and 

effects of pollutants in rivers, lakes, and estuaries, as noted in the RMOP chapter by the Panel on 

Water Pollution. Panel Chair, Gifford Ewing, also pointed out that microwave radiometers 

would be very useful in providing continuous, all-weather monitoring from satellites of both the 

sea state and temperature. Personnel at Langley were developing state-of-the-art sensors for that 

very purpose and had been demonstrating them from aircraft platforms. However, strategic 

decisions were also being made within NASA in the mid to late 1970s, regarding what research 

activities to pursue further and whether to focus the work at specific NASA “Lead Centers”. As 

an example, shortly after its success with the Mars Viking Project, Langley was not tapped for a 

new planetary exploration mission. The subsequent phase-out of planetary science studies for 

Langley was perhaps a favorable outcome, since there would not be any new planetary missions 

launched by NASA after Voyager in 1977 and until Galileo and Magellan in 1989 [Conway, 

2008]. In the late 1970s, Director Donald Hearth also decided to de-emphasize Langley’s water 

quality and microwave sensing activities, in part because it was felt that those capabilities were 

also being demonstrated effectively at JPL and Goddard. In general, further work on Earth 

imagers and microwave sounders came to a halt at Langley for the next two decades.

(a) Solar occultation 

An opportunity arose for obtaining quantitative trace species profiles from low Earth orbit (LEO) 

by the technique of making solar absorption measurements through the Earth limb. Advantages 

of solar absorption measurements are high signal-to-noise (S/N), good vertical resolution, and 
17 

excellent spectral discrimination [Russell, 1980]. Those capabilities were demonstrated by Panel 

member, C. Barney Farmer of JPL, with his balloon-borne Michelson interferometer operating 

from 1.3 to 5.5 micrometers and with funding from NASA’s Applications Program [Farmer, 

1974; Farmer et al., 1980]. Still, his co-worker, Robert Toth, found that he also had to obtain 

improved laboratory spectra for HCl and for both of its major interfering species, H2O and CH4, 

in order to obtain useful HCl profiles from the interferometer data. Thus, Toth and Farmer 

provided important updates for the line parameters of the minor and trace gas species that had 

been compiled earlier in the Air Force Cambridge Research Laboratory (AFCRL) trace gas 

catalog [McClatchey et al., 1973; Young, 1976]. NASA provided support for later versions of 

that spectral catalog, re-labeled the High Resolution Transmission molecular absorption (or 

HITRAN) database [e.g., Rothman et al., 1992]. Solar absorption survey studies were also 

conducted in 1983 using a Grille spectrometer on Spacelab 1 [Girard et al., 1988]. Balloon and 

aircraft measurements would become proof-of-concept for Farmer and his follow-on, 

Atmospheric Trace Molecule Spectroscopy (ATMOS) survey experiment that would fly 

successfully on four separate Space Shuttle missions—in 1985, 1992, 1993, and 1994 [Abrams et 

al., 1996]. ATMOS provided profile data for all the stratospheric species of interest in Section 

3a. However, ATMOS had only relatively short observing opportunities via each Shuttle flight, 

and its profiles were limited to the latitudes of their sunrise or sunset measurements. 

In the early 1970s NOAA contracted with Roland Drayson of University of Michigan for making 

feasibility studies of satellite, infrared absorption measurements of stratospheric minor 

constituents by solar occultation [Drayson et al., 1973]. They focused on those species that had 

been observed with the scanning infrared spectrometer of the University of Denver [Murcray et 

al., 1967] and for which AFCRL had already compiled molecular line parameters. However, the 

AFCRL listing of 1973 was limited to line parameters of only O3, H2O, CH4, CO, and N2O. 

NOAA personnel constructed a grating spectrometer and carried it aloft on a balloon to 39 km in 

June 1982, and they obtained useful profiles of O3, H2O, and HNO3 via solar occultation 

[Weinreb et al., 1984]. 

Somewhat earlier, Panel member, Ted Pepin, demonstrated a simple, solar occultation limbabsorption radiometer concept, Stratospheric Aerosol Monitor (SAM), as part of the ApolloSoyuz Test Project (ASTP) mission in 1975 [Pepin et al., 1977]. Based on that initial success, 

Pepin and Langley Principal Investigator, Pat McCormick, proposed for an extended 

measurement opportunity for a follow-on SAM II experiment on Nimbus 7. As originally 

proposed, they hoped to make measurements of O3 and NO2 in the visible with high vertical 

resolution (~1 km), based on Pepin’s experience with making similar measurements from highaltitude balloons when he was a graduate student of Professor Ed Ney at the University of 

Minnesota. However, the SAM II instrument was descoped to measuring only aerosol extinction 

profiles at 1-μm wavelength and at just the high latitudes because of the polar orbit of Nimbus 7. 
18 

A follow-on proposal of McCormick and Pepin was accepted for a Stratospheric Aerosol and 

Gas Experiment (SAGE) on Applications Explorer Mission B (AEM-B), having an orbital 

inclination of 55 ̊ and allowing for observations equatorward of about 65 ̊ latitude in each 

hemisphere. Their instrument was launched in February 1979, and it obtained profiles of aerosol 

extinction at 0.45 and 1.0-μm and of O3 and NO2 across those latitudes each month [McCormick 

et al., 1979]. SAGE operations continued until November 1981. McCormick and William Chu 

of Langley designed another experiment, SAGE II, for measuring O3 and NO2 and having more 

channels for characterizing both the aerosol extinction profiles and their size distributions. They 

also added a channel for inferring water vapor profiles from solar transmission measurements at 

0.94-μm. The SAGE II instrument operated from the Earth Radiation Budget Satellite (ERBS) 

that was deployed from Space Shuttle flight, STS-41G, in October 1984 with an orbital 

inclination of 57 ̊ or similar to that of SAGE I [McCormick et al., 1989]. Issues that they 

considered and addressed in successive versions of their algorithms were the absolute absorption 

cross-sections for the primary and interfering species along the limb path and a better model of 

the effects of refraction on the shape of the rising and setting Sun at the lower altitudes. SAGE II

went on to become a huge success, providing very high quality, long-term measurements of 

aerosols and O3 for nearly 21 years [Yang et al., 2006] and of H2O for the many years when its

absorption did not suffer from the large effects of the extinction by the volcanic aerosols. 

(b) Limb infrared emission 

Although solar occultation is a powerful technique for obtaining good quality profiles of a 

number of minor and trace gas species during a single sunrise or sunset event, the RMOP Panel 

realized that one could use infrared, limb emission measurements to obtain daily, near-global 

species distributions and for both day and night from a polar orbiting, Nimbus-type spacecraft. 

Such measurements offered the promise of analyzing for the global-scale effects of both 

chemistry and transport on stratospheric ozone and its related species. To demonstrate this 

possibility, the Air Force Geophysics Laboratory (AFGL) conducted a SPectral Infrared Rocket 

Experiment (SPIRE) in 1977 for the purpose of identifying species emissions from the 

atmospheric limb [Stair et al., 1985]. However, it became clear that one must also be able to 

retrieve the atmospheric temperature accurately, in order to account for its effects in the retrieval 

of a given trace species from its spectral radiance profile. Simulations showed that the 

temperature profiles from, say, the nadir-viewing SSU did not provide the vertical resolution and 

the co-located information on temperature versus pressure that is needed for the accurate 

retrieval of ozone from an individual limb radiance profile. 

An early version of the satellite limb infrared emission approach was demonstrated by Panel 

Member, John Gille, using the Limb Radiance Inversion Radiometer (LRIR), which obtained 

both temperature and ozone profiles for the stratosphere and lower mesosphere from Nimbus 6. 

In order to obtain good accuracies for single temperature and ozone profiles, Honeywell 

Radiation Center (HRC) provided cooling for the detectors and internal optics of the instrument 

to improve the S/N of the measured radiances [Kollodge et al., 1972]. Gille and House [1971] 

developed an algorithm for the retrieval of stratospheric temperature-versus-pressure or T(p)
19 

profiles using a spectrally-narrow channel, plus another much broader, radiometer channel 

centered on the 15-μm bands of CO2. Their T(p) profiles were then used for the retrieval of the 

co-located ozone mixing ratio profiles from the LRIR radiance measurements near 9.6-μm

[Gille, 1979]. Even so, the accuracies of the retrieved temperatures and, in particular, ozone 

were limited by an inexact knowledge of the spectral line parameters of O3 at both 9.6 and 14.1-

μm. In fact, one could say that the taking of solar occultation and/or infrared limb emission 

measurements was analogous to carrying out spectroscopic studies of a target molecule, where 

the atmospheric limb itself is substituted for the laboratory cell path and pressures. 

A disadvantage of limb sounders that the Panel noted is that one must know where the 

instrument is pointing along the horizon with high accuracy. Detector noise can be a limitation 

for a radiance scan at the higher altitudes, where the radiances are becoming small. The LRIR 

instrument had internal reflections which compromised the ability to retrieve useful H2O profiles 

from the LRIR radiances in the rotational band near 25 μm of its channel. Improvements in 

detector technology, the cooling of optical arrays, a decrease of the horizon scan rate, and more 

extensive pre-flight calibrations were all considered for limb-viewing instruments on Nimbus 7 

and beyond, in order to achieve better S/N and to characterize the effects of spurious radiance

from within the instrument itself.

 

At this point the reader is reminded that the findings and recommendations of the RMOP Panel 

did not really impact NASA’s selection of rocket and satellite instruments prior to Nimbus 7, 

although the performance of those early instruments provided very useful information for the 

improved designs and alternate concepts for future Earth observing satellites. As an example, 

Langley researchers, John Dodgen, Howard Curfman, Antony Jalink, Jr., Richard Davis, and 

Thomas McKee conducted important measurements during the 1960s for sensing the Earth’s 

horizon in support of spacecraft guidance and navigation studies and ultimately for preparations 

of the controlled re-entry of manned capsules into the Earth’s atmosphere. In particular, they 

made initial measurements of the horizon with a four-channel radiometer (uv, visible, and near 

and middle infrared bands) on a Javelin rocket flight from Wallops Island in 1961 [McKee et al., 

1964]. Hanel et al. [1963] of Goddard had made calculations of the infrared horizon for 5 

separate spectral intervals in the infrared and concluded that the 15-μm region of CO2 was the

most suitable for a horizon sensor. Subsequently, Bandeen et al. [1963] verified those findings 

using measured horizon radiances from the medium resolution scanning radiometer on TIROS 

VII. Langley personnel initiated their Project Scanner in 1963 for the purpose of developing a 

more efficient horizon sensor based on radiances in the 15-μm bands. Two suborbital, ballistic 

rocket flights of a radiometer were made in 1966 to characterize the infrared signature of the 

horizon and eventually for obtaining accurate temperature profiles [McKee et al., 1969; House 

and Ohring, 1969]. Another aspect that they considered was how to account for the horizontal 

gradients in atmospheric temperature (and CO2 radiance) along the tangent path of the 

measurements, especially for the winter hemisphere [Davis, 1969]. 
20 

Those early horizon definition studies led to a high altitude balloon flight of the AAFE 

instrument, Lower Atmospheric Composition and Temperature Experiment (or balloon 

LACATE), on May 5, 1974, at the White Sands Missile Range, New Mexico, for the further 

measurement of the stratospheric minor gases, H2O and O3, and of the trace gases, HNO3 and 

NO2, that interact with ozone. Unfortunately, useful retrievals of their profiles from the 

LACATE radiances were hindered by an inadequate knowledge of the pointing attitude for

sensors on the balloon platform. Nevertheless, balloon LACATE became the precursor to the 

Limb Infrared Monitor of the Stratosphere (LIMS) experiment launched on Nimbus 7 in October 

1978. Analyses of the radiance profiles from LACATE revealed that they were contaminated 

slightly by reflected radiances, internal to the instrument itself. That experience led to further 

internal baffling and test calibration measurements for the LIMS radiometer, prior to its launch. 

LIMS operated for the planned 7+ month lifetime of the cryogen gases for its detectors. It 

provided measurements of temperature and O3 and near-global profiles of stratospheric NO2, 

HNO3, and H2O—primary objectives of the RMOP Panel as summarized in Section 3a. The 

quality of the retrieved LIMS temperature and species profiles was assessed by comparisons with 

rocket and balloon measurements during the mission life of LIMS [Gille and Russell, 1984, and 

references therein]. Such correlative measurement opportunities were designed by the NASA 

program and project managers to ensure the success of all the experiments on the Nimbus 7 

“pollution patrol” satellite, as urged by the RMOP Panel. 

Although the broad-band, limb radiometer approaches of LRIR and LIMS were limited by an

inadequate, direct knowledge of the attitude and pointing of the Nimbus 6 and 7 spacecraft, the 

LIMS principal investigators, Gille and Jim Russell III (Panel member from Langley), 

successfully employed the so-called “two color method” of Gille and House [1971] for the 

retrieval of good quality T(p) profiles. One drawback for applying this method with LIMS was 

that one must have a good first-order, estimate of the atmospheric ozone because its 14-μm ν2

band interferes significantly with the broad-band radiances of the LIMS CO2 channels that were 

used to retrieve T(p). A first pass of the retrieval algorithms was used to obtain the horizontal 

temperature gradients and a reasonable estimate of the interfering ozone, followed by a second 

pass to obtain the final temperature and species profiles [Remsberg et al., 2004]. LIMS provided 

good quality profiles of H2O and HNO3, and also of O3, at least after improved ozone line 

parameters became available in 1982 for its retrieval. On the other hand, this broadband 

radiometer approach is limited to the relative handful of trace species that do not suffer the large, 

spectral overlapping of their radiances by other gases. For instance, the goal of good quality 

NO2 profiles for the lower stratosphere was limited by a spectral overlap with emissions from 

H2O and from the O2 continuum [Russell et al., 1984]. The LIMS-retrieved NO2 was also biased 

high in the upper stratosphere due to a lack of knowledge in 1979 of the spin-splitting effects for 

its nearly-saturated, strong lines. After accounting for those effects, Remsberg et al. [2010] were 

able to achieve reasonably accurate profiles of NO2, as well. 

Goody [1968] demonstrated that one can use a gas correlation infrared spectrometer to identify 

the trace gas N2O in the presence of an interfering ammonia gas, whose absorption lines are 

much stronger than those of the target N2O gas in the PMR cell. By employing instrument cells 
21 

of differing internal pressures one can make use of the pressure-broadened line shapes of the 

known amounts of the target gas in each of several instrument cells for a retrieval of the 

atmospheric trace gas profile from its measured radiances. With this approach the companion 

Nimbus 7 SAMS limb-viewing experiment [Drummond et al., 1980] provided for the first time 

the near-global scale distributions of CH4 and N2O with a vertical resolution of about 8 km. 

These source gases are converted chemically to H2O and NOx, as noted by the RMOP Panel (see 

Section 3a). The SAMS measurements of these two tracer-like gases gave an excellent 

indication of the large-scale seasonal and interannual transport within the mid-stratosphere 

[Jones and Pyle, 1984]. Further details about the daily variations of those species about their 

zonal means were limited, however, by the relatively low S/N of the individual radiance profile 

measurements from the PMR channels of SAMS. The low S/N was because it was decided to 

apply passive cooling methods to the SAMS channels, rather than be limited by the lifetime of 

the cryogen-gas coolers that were available at that time. Drummond hoped to obtain several 

years of data, at least. But because the passive radiation cooler did not achieve its design 

temperature, it was only possible for SAMS to provide zonally-averaged results for the gases CO 

at 4.7 μm, NO at 7.7 μm, and the CO2 channel radiance at 4.3 μm [Taylor et al., 1981]. Cooled 

detectors would correct for that problem in an Improved SAMS (or ISAMS) experiment for a 

follow-on NASA research satellite, but not scheduled for launch until 10 years later (Section 6). 

(c) Partial column ultraviolet scattering and absorption 

Heath et al. [1975] developed a double uv-monochrometer instrument for Nimbus 7. Similar to

the Nimbus 4 BUV, their solar backscatter ultraviolet (SBUV) experiment had 8 short 

wavelength channels for inferring the ozone profile above the main ozone density maximum and 

4 longer wavelength channels for determining total atmospheric ozone [McPeters et al., 1984]. 

SBUV operated successfully from its launch in 1978 and until June 1990, and it appeared that 

the losses of ozone in the upper stratosphere were occurring at an alarming rate. Early on

though, Robert Hudson of Goddard concluded that there was some degradation of the reflectivity 

of the diffuser plate of the SBUV instrument, which led to a more extensive set of independent 

verifications of the total ozone measurements from SBUV based on comparisons with groundbased Dobson station data and later on with Shuttle-borne or SSBUV instruments.

At the same time NASA and the ozone research community wanted to verify that the SBUV, 

LIMS, and SAGE ozone profile measurements were of high quality and accurate. To that end, 

Upper Atmosphere Research Program (UARP) managers, Shelby Tilford and Robert Watson, 

also sponsored several balloon-ozone, intercomparison campaigns (BOIC) from its launch 

facility in Palestine, Texas, for the several in situ ozone instruments that were part of their 

extensive, satellite ozone validation activities. More broadly, the various aircraft, balloon, and 

rocket ozone measurement programs of NASA and NOAA were designed to ensure that the 

atmospheric modeling community could be confident about the changes that they were 

predicting for the ozone. Their findings were also critical for an assessment of the related policy 

implications. NASA also provided support for laboratory studies of the key rates of the chemical 

reactions that affect the vertical distribution of ozone, a key factor in bringing about better 
22 

agreement between observations and the chemical model results. Those updated rates formed 

the basis of the periodic JPL publications on the chemical kinetics and photochemical data for 

use in atmospheric studies [e.g., JPL Publication 09-31, 2010]. 

Adarsh Deepak and M. P. McCormick held a workshop in December 1976 on inversion methods 

for the atmospheric remote sounding data, supported by Morris Tepper and J. D. Lawrence 

[Deepak, 1977; Lenoble, 1977]. This gathering of the experts on retrieval methods was very 

timely for the selection, demonstration, and deployment of Earth-observing experiments like 

SBUV and the monitoring of ozone from operational satellites. Such ozone datasets would 

become critical to the periodic, World Meteorological Organization (WMO) ozone assessment 

reports and for the verification of climate/chemistry models of stratospheric ozone. Retrieval 

algorithms for the NASA SBUV and later the NOAA-based SBUV/2 ozone instrument profiles 

rely on the optimal estimation approach of Mateer [1977] and later of Rodgers [1990]. They 

showed that middle and upper stratospheric ozone could be determined with high accuracy and 

moderate vertical resolution, but that the quality of the retrieved partial column ozone of the 

lower stratosphere required information from the total ozone channels of SBUV and an estimate 

of the ozone profile shape below its density maximum—obtained later with the aid of the ozone 

profile data from SAGE.

Nimbus 7 also carried onboard the cross-track scanning, Total Ozone Mapping Spectrometer 

(TOMS), a space borne uv-monochrometer, which is the equivalent of the ground-based Dobson 

total ozone instrument [Heath et al., 1978; Bhartia et al., 1984]. TOMS ozone images were 

produced daily by NASA Goddard, and they are recognized widely as the primary visual 

measure of the variations of the Earth’s ozone layer and later as a clear indicator of the extent of 

the Antarctic “ozone hole” in springtime [e.g., Schoeberl et al., 1986]. The development, testing, 

calibration, and deployment of the succession of TOMS instruments was a direct outgrowth of 

NASA’s mandate under the Clean Air Act Amendments of 1977 and of the charge of the RMOP 

Panel, “that any changes in total ozone be monitored, and causes be identified.” For example, 

the Panel wanted to be able to know yearly average total ozone to within 1%. However, the 

concerns about total ozone by the Panel were not limited by what might happen to its 

stratospheric layer, but also extended to the effects of tropospheric pollution on the regional and 

global scale ozone. As a result, a most important issue would soon become how to know about 

any changes in the long-term calibration of the TOMS instrument, as well as to understand how 

to splice together the long-term data records from a series of operational TOMS-like instruments.

A related part of the early horizon definition programs was to verify theoretical studies of the 

Earth’s horizon in the ultraviolet and visible by analyzing the data taken with photometers 

aboard test rockets and the X-15 research aircraft by Langley [e.g., Hrasky and McKee, 1964]. 

Later, Malchow and Whitney [1977] of the MIT Draper Laboratory with support from NASA’s 

AAFE Program explored the information content of visible, limb scattering and absorption 

measurements and the conduct of retrievals of stratospheric ozone and NO2. In fact, photometric 
23 

measurements of this kind were also obtained from Skylab in 1973, although their calibrations 

were deemed inadequate for a proper testing of the associated retrieval algorithms. In October 

1981 NASA/JPL launched into orbit the Solar Mesosphere Explorer (SME) satellite experiment 

of Charles Barth of the University of Colorado (and formerly of JPL) for obtaining profiles of 

ozone, NO2 and H2O using the uv-visible and 1.27-μm limb scattering techniques [Barth et al., 

1983]. SME obtained 4 years of quality ozone profiles from about 50 to 80 km and with a 

vertical resolution of order 4 km, and those data were used to verify chemical models of the 

ozone in the mesosphere. Aruga and Heath [1982] considered an extension of the limb scattering 

approach of MIT for the measurement of ozone from the altitude range of 70 to near 20 km, or 

down to where the SBUV partial columns contain less detail and attain a vertical resolution of 

only 10 to 15 km. However, the proof-of-concept of their technique in the presence of 

stratospheric aerosol layers would not be demonstrated clearly until much later (see Section 7). 

(d) Correlation radiometry and active sensing for tropospheric species 

Because of the concerns about ozone that were paramount in the 1970s, the development of 

satellite-borne remote sensors by NASA was focused mostly on the several key parameters and 

species that might affect it. However, there was also interest and concern about what changes 

might be occurring for the chemistry of the troposphere. The NASA Office of Space and 

Terrestrial Applications (OSTA) and Langley’s EQPO sponsored a series of lectures on the topic 

in 1977 to revisit the scientific imperatives for an understanding of the chemistry of the 

troposphere [Levine and Schryer, 1978]. The RMOP Panel knew that making such 

measurements from a satellite would not be easy. Nevertheless, the feasibility of observing air 

pollutants in the troposphere with satellite-borne sensors was considered in the early 1970s by 

Panel member, Claus Ludwig, and colleagues [Ludwig et al., 1974], and the prospects for one 

species mentioned in Section 3a looked quite promising—carbon monoxide (CO). In the mid 

1970s Harold Goldstein of General Electric and Peter Lebel of Langley conducted measurements 

of CO and CH4 with the Carbon Monoxide Pollution Experiment (COPE) correlation 

interferometer near 2.3 μm from an aircraft with support from the AAFE Program. COPE gave 

atmospheric column density measurements of CO and their values were verified with profiles 

obtained with in situ samplers. In fact, such validation activities were the impetus for NASA 

and, in particular, Langley’s airborne tropospheric field campaigns of the next several decades.

RMOP Panel Co-Chair, Henry Reichle of Langley, went on to lead the development of a gas 

filter correlation radiometer operating at 4.7 μm for making measurements of column CO from 

both an aircraft platform and eventually on the second engineering test flight of the Space Shuttle 

(STS-2) in 1981 [Reichle et al., 1986]. His concept became known as the Measurement of Air 

Pollution from Satellites (MAPS), and he would fly it again on Shuttle in 1984 and twice in 1994 

[Newell et al., 1999]. MAPS provided low vertical resolution profiles of tropospheric CO across 

the low and middle latitudes. Newell et al. [1999] found that high levels of CO were associated 

with regions of biomass burning. They also reported finding low values of upper tropospheric 

CO associated with relatively high values of potential vorticity, suggesting that those air samples 

originated from the stratosphere. The MAPS measurements were really the first demonstration 
24 

that one could anticipate conducting studies of extended layers of atmospheric pollution from a 

satellite platform, and they would lead to more concerted attempts during the EOS era. The 

measurement of tropospheric column ozone or ozone profiles from a satellite platform was also 

considered in the 1970s and 1980s, with an emphasis on active sensing techniques. 

J. D. Lawrence, Jr., M. P. McCormick, and S. H. Melfi of Langley’s Instrument Research 

Division (IRD) had conducted laser backscatter measurements in the late 1960s for the purpose 

of sensing turbulent regions of the atmosphere. They also reported evidence of Raman scattering 

by H2O in the lower atmosphere and by SO2 in a smoke plume from a power generating plant 

[Melfi et al., 1969; Melfi et al., 1973]. Quantitative Raman measurements of SO2 were 

demonstrated subsequently by Poultney et al. [1977]. However, it was clear that the Raman 

scattered signals were much too weak to be considered for remote sensing of tropospheric gases 

using a laser system operating from a space platform. Instead, Langley and JPL supported study 

contracts in the 1970s to determine the technology investments that would be needed for 

conducting profile measurements in the troposphere using the concept of a differential absorption 

lidar (DIAL) from a Space Shuttle platform. It soon became clear that accurate profile 

measurements of tropospheric H2O ought to be possible from Space. Remsberg and Gordley 

[1978] noted that DIAL would not be as feasible for measuring tropospheric ozone because of 

the attenuation of its tropospheric return signals by the much larger column ozone amounts of the 

stratosphere. It would be necessary to tune the DIAL system to several pairs of absorbing and 

non-absorbing uv-wavelengths. Several years later, Ed Browell of Langley led an international 

working group of experts in assessing in more detail what gas species might be sensed with laser 

systems operating from Space [NASA, 1979]. Over the next several decades those prospects

became more fully realized with the development and demonstration of the use of stable, tunable 

laser systems in a number of airborne field campaigns focused on regional studies of ozone in the 

troposphere and even into the lower stratosphere. The performance of the Langley airborne uvDIAL system also demonstrated that it is certainly possible to obtain useful measurements of the 

regional-scale variations of tropospheric ozone from low Earth orbit and with an altitude 

resolution of order 2 km [Browell et al., 1998]. 
25 

6 Changing priorities and technology advancements (1986-1996) 

(a) Science and politics

In the 1980s the nation was coping with the ravages of inflation following the Vietnam War. 

There was also a decrease in public awareness and support within the U.S. regarding 

environmental issues. The Reagan administration put limits on the research and enforcement 

activities of the EPA and reduced funding within the NASA Earth applications programs. 

Government support waned within NOAA and NASA for enhancing the satellite technology, 

especially following the recession of 1982. There was a contraction of NASA’s engineering and 

technician workforce, and there were greater incentives for their activities to be undertaken by 

contractors or entirely by the private sector in some instances. Thus, it was a time of adjustment 

and retrenchment for NASA. Opportunities were few for actually demonstrating instrument 

concepts from satellite orbit. Investments in new technologies also dwindled, and the proof-ofconcept of measurements from low Earth orbit had to be carried out from the Space Shuttle. As 

a consequence, instrument performance was often demonstrated from aircraft and balloon 

platforms, as part of field campaigns focused on gaining an understanding of the budgets of trace 

chemicals in the troposphere. Further, in the late 1980s and early 1990s the Reagan and Bush 

administrations opted to move away from the Space Shuttle as a primary delivery vehicle for 

satellites to low Earth orbit. Instead, they envisioned using it to construct the International Space 

Station (ISS) and to have it as an intermediate staging platform for sending probes to Mars and 

beyond. 

Effects of man-made compounds from SST exhaust plumes and due to the release of CFC

compounds into the atmosphere continued to be a paramount concern of atmospheric scientists 

during this period because of their potential effects on stratospheric ozone. It was clear that the 

measurement technologies to be adopted would be based on their ability to both characterize the 

natural stratosphere and to understand the effects of pollutant perturbations to its chemical 

makeup. The culture for Earth Science research also changed within NASA. Prospective, inhouse science and technology studies were selected as a result of positive reviews from the 

external peer community, in large part. Langley continued to focus on the development of 

sensing technologies for the study of stratospheric ozone because that knowledge was important 

for clarifying what role questions about ozone might play in the further development of high 

speed civil transport (HSCT) aircraft at Langley and the potential role of such aircraft for the 

international trade balance of the U. S. Sorting out the role of man-made versus natural forcings 

for Earth’s climate was also becoming an area of interest within NASA. For instance, 

stratospheric aerosol layers from the eruptions of Mt. St. Helens in 1980 and from the much 

larger eruption of El Chichon in 1982 were easily detected and monitored with the SAM II and 

SAGE satellite instruments by Langley researchers. It was also known that such volcanic 

aerosol layers led to a temporary cooling of surface temperatures, at least for those latitude zones 

where the volcanic aerosol optical depth was greatest.
26 

The major NASA Earth Science satellite initiative during the 1980s was the Upper Atmosphere 

Research Satellite (UARS) with a large payload of twelve separate experiments. UARS carried 

four experiments focused on improving our understanding of the effects of chemistry and 

transport on stratospheric ozone [Reber et al., 1993]. They included the Halogen Occultation 

Experiment (HALOE) [Russell et al., 1993], the Cryogenic Limb Array Etalon Spectrometer or 

CLAES [Roche et al., 1993], the Microwave Limb Sounder (MLS) [Waters et al., 1996, and 

references therein], and the ISAMS instrument [Taylor et al., 1993]. RMOP Panel member,

James Russell III, proposed HALOE for obtaining near-global measurements of HCl and HF 

profiles plus a number of other species, including ozone itself. HCl and HF are the end products 

of the chemistry of halogen compounds in the stratosphere. His concept for HALOE was 

developed under the AAFE Program, and it was demonstrated through flight tests of a 

brassboard instrument on the CV-990 research aircraft. HALOE employed both broadband 

infrared radiometry and gas filter correlation radiometry for obtaining single profiles of a number 

of trace gas species via solar occultation. The CLAES and ISAMS experiments together 

measured the primary chlorofluorocarbon source molecules plus a number of molecules that 

were used to isolate the roles of the several chemical families on the ozone profile. CLAES 

relied on cooled detector arrays and very narrow spectral intervals for its measurements. ISAMS 

obtained nine months of good data before its chopper mechanism failed. More importantly, 

UARS carried MLS for measurements of chlorine monoxide (ClO), ozone, and other related 

species using millimeter-wavelength, thermal emission heterodyne techniques. The development 

and demonstration of the ground-based and airborne versions of MLS were also supported under 

the AAFE Program, as urged by the members of the RMOP Panel.

The goal of achieving accurate species profile measurements with adequate vertical resolutions 

was pursued by the satellite remote sensing community as early as 1975, prior to the launch of 

Nimbus 7 and before demonstrations of the success or deficiencies of its sensors. In fact, the 

MAPS experiment concept had also been proposed for Nimbus 7, but it was concluded that the 

MAPS gas filter technology and algorithms were not yet sufficiently mature. At about that time 

Russell et al. [1977] recognized that it would be feasible to use gas filter spectroscopy for the 

measurement of stratospheric halogen compounds via solar occultation. In addition, Park et al. 

[1980] developed methods for obtaining co-located T(p) profiles for the vertical registration of 

the transmission profiles from the HALOE channels. They proposed using a narrow band 

radiometer operating in the 4.3-μm region of CO2 for that purpose. 

All four stratospheric experiments on UARS took advantage of the improved vertical resolution 

of the long atmospheric path offered by a limb-viewing geometry. S/N was increased by the use 

of cooled detectors having longer cryogen lifetimes or a Stirling-cycle refrigerator for CLAES 

and ISAMS, respectively. CLAES measurements were made at focused, narrow spectral 

intervals to reduce the effects of radiances from unwanted, interfering species. During late 1991 

and early 1992 the measurements from SAGE II and from the HALOE, ISAMS, and CLAES 

experiments were affected by the stratospheric aerosols from the eruption of Mt. Pinatubo, which 

occurred in June 1991 or three months prior to the launch of UARS. Most fortunately, the MLS 

measurements were unaffected by the interfering volcanic aerosols. 
27 

The disastrous Shuttle Challenger accident occurred on January 28, 1986, bringing about a twoyear hiatus before there would be any further launches of the Space Shuttle. UARS had been 

scheduled for a launch from Shuttle in 1989, but it was not placed into Earth orbit until 

September 1991. Earlier it was noted that the hiring of atmospheric remote sensing specialists 

was very limited within NASA during the 1970s and 1980s. Most of the instrument 

development work was conducted by civil servants upon being re-directed from other activities 

that had been de-emphasized following the Apollo era. HALOE was Langley’s contribution to 

UARS. By having a workforce that was focused on specific technologies, it was possible for 

Langley to bring HALOE in-house eventually and complete its fabrication. The two-year launch 

delay also meant that there was more time for conducting additional tests and calibrations of 

HALOE. Those additional studies of the performance of HALOE were very helpful for a proper 

characterization of the 14-year time series of its atmospheric species and temperature profiles.

To stay abreast of the advancing measurement technologies, Langley, Goddard, Ames, and JPL 

hired contractors during this period to help with the development and demonstration of new or 

improved sensors for Earth applications. At Langley they contributed to the SAGE II, HALOE, 

MAPS, and ISAMS Projects, both prior to and following their launch. Several of those 

contractors were hired later as NASA researchers or technologists. They include Mike Pitts, 

Larry Thomason, Chip Trepte, and Joe Zawodny with SAGE II, Marty Mlynczak, Jae Park, 

Curtis Rinsland, and Mary Ann Smith with HALOE, and Estelle Condon, Pamela Rinsland, and 

Vickie Connors with MAPS. Brian Connor contributed to ISAMS and led its ozone validation 

paper [Connor et al., 1996]. Still, much of the Project work was performed by dedicated 

contractors at Systems and Applied Sciences Corp. (SASC), Hughes STX, Corp., Science and 

Technology Corp. (STC), Science Applications International Corp. (SAIC), Gordley and 

Associates Technical Software (GATS, Inc.), and PRC Kentron, Inc., as well as The College of 

William and Mary and Old Dominion University.

(b) The “Antarctic ozone hole” and trends in global ozone

Prior to 1985 and before the measurements from UARS, the likely effects of reactive chlorine on 

upper stratospheric ozone had become understood reasonably well based on ground-based 

microwave measurements of both ClO and O3 by Joe Waters and on the multiple balloon-borne 

soundings of the CFC source molecules by NOAA and NASA. The U. S. subsequently banned 

its use of CFCs as propellants, and the political conflict over stratospheric ozone cooled down 

considerably [Conway, 2008]. As is normally the case however, scientific priorities often 

change before it is possible to develop a measurement concept and demonstrate its promise from 

an Earth orbiting research satellite. The announced discovery of an “Antarctic ozone hole” in 

1985 plus NASA’s mandate to monitor the health of the ozone layer as part of the CAA 

amendments of 1977 meant that there was an even greater urgency for understanding this 

unanticipated loss of polar ozone and for developing a strategy to reverse it, if possible. 

Fortunately, much of the measurement technology that had been developed and tested under the 
28 

AAFE Program was available for making more focused sets of polar ozone measurements from 

NASA research aircraft. Those airborne campaigns were conducted in conjunction with the 

ongoing observations at ground-based sites in Antarctica and in the Arctic that were supported 

by NOAA and the National Science Foundation (NSF). Data obtained with the TOMS, SBUV, 

SAGE II, and ATMOS experiments were also available for studying the “Antarctic ozone hole”. 

Initial findings from those satellite data sets are reviewed in Russell and McCormick [1987]. 

Thus, the focus on ozone with UARS moved from the upper stratosphere to the lowermost 

stratosphere and to what was happening at polar latitudes, in particular. It also meant that 

heterogeneous chemical processes must be incorporated into chemical models of the ozone and 

verified with measurements. A comprehensive summary of the “Antarctic ozone hole” issue can 

be found in Solomon [1999]. 

The two primary sources of bias error for satellite remote sensors are due to an inadequate 

knowledge of the satellite (and sensor) orbital attitude and to their co-located temperature 

profiles, particularly for thermal infrared measurements. Findings from the early infrared 

horizon sensors of Langley’s Project Scanner, from radiance modeling studies, and from the 

TIROS and Nimbus research satellites indicated the need for even better capabilities for Earthreferenced, in-flight controls and for the instrument attitude and pointing of UARS [Phenneger et 

al., 1985]. Improved retrievals of the temperature versus pressure or T(p) profiles were also 

attained as a result of more accurate forward models for their CO2 radiance and/or transmission 

profiles. Forward models for the minor and trace species of UARS benefitted from 

improvements in the line parameters of the target gases and their interfering species, particularly 

those of CH4 for the retrieval of HCl from HALOE. In general, comparisons of the UARS 

measurements with those from independent techniques showed that the species profiles from 

UARS are reasonably accurate, as well as precise. Even for SAGE II, it was found that a better 

accounting for the secondary effects of the ozone cross section at 0.935 μm plus an adjustment 

for a “spectral drift” of the interference filter of that channel gave improved profiles and trends 

for lower stratospheric H2O in its Version 6.2 dataset [Thomason et al., 2004]. Thus, even 

though SAGE II and the several experiments on UARS were designed to acquire important 

information about the effects of chlorine radicals on upper stratospheric ozone, their 

measurements became focused primarily on the issue of Antarctic ozone depletion. 

From the mid-1980s onward, another scientific measurement requirement was presented to the 

remote sensing community because of the effects of reactive chlorine on the ozone profile that 

had been realized for both the upper stratosphere and for the polar regions of the lower 

stratosphere. Specifically, could the trends in ozone and the parameters that control it be 

measured with the accuracies that were needed? Because instruments on research satellites like 

Nimbus 7 were not designed with that goal in mind, it was necessary to re-consider how well 

each instrument was calibrated over time and whether any orbital changes for their parent

spacecraft might affect their derived trends. Frederick and Serafino [1985] anticipated such 

requirements for the operational SBUV sensors, for example. Soon thereafter, Harold Johnston 

of University of California, Berkeley, chaired an Ozone Trends Panel for NASA. That Panel 

issued a report of findings that led to new activities within the satellite remote sensing 
29 

community for the monitoring of both temperature and ozone [WMO, 1988]. In general, they 

concluded that satellite, solar occultation instruments ought to be able to provide reliable trends, 

primarily because they have an exoatmospheric calibration for each sunrise or sunset profile and 

because there is less of a chance for a long-term change in their instrument components. One 

exception is the possibility for degradation in the characteristics of the interference filters. 

Another related requirement for quantifying changes in the distributions of species from multiple 

satellites is to know that each of the separate datasets have been processed using the same 

version of the spectral line parameters for a given species. This latter requirement might mean 

that a reprocessing of an early dataset would need to be undertaken, in order to compare it with 

the data from a follow-on experiment. For the TOMS and SBUV sensors, significant efforts 

were devoted toward just how to account for discontinuities in the datasets from a succession of 

those instruments [e.g., Hilsenrath et al., 1995]. Miller et al. [1997] confirmed that the SBUV 

and Umkehr measurements are only able to quantify the long-term variations of ozone for the 

middle to upper stratosphere. The RMOP Panel did not really foresee or address such

circumstances for the assessment of ozone trends in its report of 1971, although they did lay the 

groundwork for conducting further studies of any instrument related issues. 

Since reliability was uncertain for the trends in remotely-sensed ozone and related species from 

the early satellite measurements, NASA became involved in 1991 in what is now known as the 

international Network for the Detection of Atmospheric Composition Change (NDACC), 

presently co-chaired by Geir Braathen of WMO and Mike Kurylo, a former NASA Program 

Manager. In some respects NDACC is a replacement for the Meteorological Rocket Network 

(MRN) and its routine soundings of the state of the middle atmosphere. The NDACC consists 

primarily of ground-based remote sensors, some of which were being developed and 

demonstrated at the time of the RMOP Report. They include Rayleigh backscatter (temperature 

and aerosols), sodium vapor fluorescence (temperature), DIAL (ozone and aerosols), and Raman 

(water vapor) lidar systems, microwave radiometers (ozone, water vapor, and ClO profiles), 

uv/visible and Fourier Transform Infrared (FTIR) spectrometers (for measuring column content 

of a number of trace species), and Dobson instruments (total column ozone). In fact, Remsberg 

[1986] made early use of Rayleigh lidar soundings from the French lidar group of Marie-Lise 

Chanin for his validation study of the quality of the LIMS temperature profiles of the upper 

stratosphere and lower mesosphere. Brian Connor of Langley, Rich Bevilacqua and Gerald 

Nedoluha of the Naval Research Laboratory), John Olivero of Penn State University (but 

originally at Langley), Alan Parrish of University of Massachusetts, and Phil Solomon of State 

University of New York (SUNY) at Stony Brook, conducted ground-based microwave 

measurements of species profiles from California, Hawaii, New Zealand, and at McMurdo 

Station, Antarctica, in support of UARS. Curtis Rinsland, Joel Levine, and Thomas Miles of 

Langley analyzed for long-term trends in the tropospheric species, CO and CH4, from time series 

of solar spectra taken since 1951 from the Jungfraujoch Observatory in Switzerland [Rinsland 

and Levine, 1985; Rinsland et al., 1985]. Long-term variations of ozone, H2O, and temperature 

from NDACC station data are still serving as an independent check of the findings from the 

satellite data records [Steinbrecht et al., 2009]. 

 
30 

During the late 1980s and early 1990s there was renewed interest within the U. S. aircraft 

industry toward a HSCT plane that would fly more quickly to the countries on the “Pacific Rim”, 

as well as to Europe or to the Middle East and India. Studies were instituted in the early 1990s 

by Howard Wesoky of NASA’s Office of Aeronautics and Space Technology (OAST) about the 

likely effects of HSCT emissions on the atmosphere and on the prospects for cleaner engine 

combustion technologies in reducing those emissions. The early work of the RMOP Panel was 

still relevant to that activity because much of the original purpose of the Panel arose out of 

similar concerns in 1971 about the effects of emissions from SST aircraft. NASA formed a High 

Speed Research Project (HSRP) Office at Langley and assigned Alan Wilhite to manage its

activities. Richard Stolarski of Goddard led an associated Panel in a study of the Atmospheric 

Effects of Stratospheric Aircraft (AESA). In fact, the combined HSRP/AESA provided most of 

the support for the atmospheric assessment models that would be used to predict environmental 

impacts of a fleet of the supersonic planes. European researchers conducted their own studies 

but with a focus on the effects of the current and future subsonic fleet. Of course, there were 

also concerns about the effects of their additional emissions on polar ozone, particularly from 

trans-oceanic flights across the high northern latitudes. With that in mind, NASA sponsored 

several comprehensive model/measurement (M&M) study activities, including comparisons with 

the remotely-sensed, distributions of ozone and its related chemical species from UARS. 

HSRP/AESA also supported laboratory studies of the heterogeneous processes that affect polar 

ozone. 

The combined HSRP/AESA program assisted with further developments in remote sensing 

technologies and their demonstrations for the stratosphere and troposphere, as carried out during 

dedicated NASA airborne research campaigns and from studies of aircraft emissions and their 

related tropospheric species. For example, Langley researchers, Glenn Sachse and Glen Diskin, 

conducted airborne species measurements using gas filter correlation and tunable diode laser 

techniques. Ed Browell and co-workers made DIAL lidar measurements of ozone and aerosols 

from a DC-8 aircraft. Bruce Anderson conducted in-flight measurements of the gaseous and 

particulate aircraft emissions injected to the atmosphere. There was also a succession of airborne 

campaigns as part of NASA’s larger Global Tropospheric Experiment (GTE) program, managed 

by Joe McNeal. GTE activities at Langley were managed by John Mugler, Robert Harriss, 

James Hoell, Richard Bendura, and James Crawford. Many of the initial airborne test flights

were assisted by personnel at the NASA Wallops Flight Facility, as envisioned earlier by the 

RMOP panel members. Demonstrations of the sensor technologies within GTE provided the 

foundation for the subsequent satellite instrument validation activities that would be needed in 

the upcoming EOS era and for studies of any trends in tropospheric ozone. 

Jack Fishman of Langley was the first to suggest that photochemical ozone production in the 

troposphere can be inferred for the tropics from an analysis of TOMS total ozone data [Fishman 

et al., 1986]. He found a positive correlation between the MAPS CO and TOMS total ozone 

values at low latitudes, related to regions of biomass burning. Fishman and Larsen [1987] went 

further and obtained estimates of the spatial variations in the tropospheric ozone column by 

integrating the stratospheric ozone profiles above the tropopause from SAGE profiles and then 
31 

subtracting those column amounts from the co-located TOMS total ozone. They would later 

show that enhancements for their so-called “tropospheric ozone residual (or TOR)” also 

indicated that there was in situ production of ozone resulting from large-scale, biomass burning 

activities [Fishman, et al., 2003]. The amount of the TOMS total column ozone that resides in 

the troposphere is only of order 10-15%. Thus, the calculation of TOR is affected by even small 

errors in the stratosphere ozone column from SAGE and in the total ozone from TOMS. Earlier, 

Remsberg et al. [1984] used a similar bootstrap method for a validation of stratospheric ozone 

from LIMS. Their approach was to find co-located ozonesonde and LIMS profiles, integrate the 

LIMS ozone profile above the 70-hPa level in the stratosphere, and then to add that amount to 

the integrated ozonesonde values from the ground to 70 hPa. Their combined sums were then 

compared with the ground-based Dobson total ozone value at the location of the sonde 

measurement. On average, the LIMS plus ozonesonde sum agreed with the Dobson data to 0.8% 

with a root-mean-square (RMS) difference of 5.4%. However, positive biases in the LIMS 

ozone were apparent in the lowest parts of the stratosphere, such that the LIMS data could not be 

used reliably to generate daily maps of the zonal variations in the TOR.

Other nations were developing and deploying their own Earth observation satellites during this 

period. Their contributions are mentioned here only briefly; the reader should consult the 

associated experiment websites and/or published articles for more details. For example, the 

European Space Agency (ESA) launched two European Remote Sensing satellites, ERS-1 and 

ERS-2, respectively, in 1991 and 1995. In particular, the Global Ozone Monitoring Experiment 

(GOME) sensor on ERS-2 was a nadir-scanning uv, visible, and near infrared spectrometer for 

measuring total ozone and column amounts of NO2 and for detecting other tropospheric trace 

gases [Burrows et al., 1999]. GOME represented a significant next step for making global 

measurements in the troposphere, and it was followed in 2006 by a second generation instrument 

on the MetOp satellite. Column ozone measurements were continued with the deployment of 

TOMS instruments on the Meteor-3 spacecraft in 1991 and on Earth Probes (EP-TOMS) in 

1996, as well as with copies of the SBUV sensor on the series of NOAA operational satellites. 

The Polar Ozone and Aerosol Measurement (POAM II and III) experiments of NRL were 

launched on the French SPOT 3 and 4 spacecraft in 1993 and 1998, respectively. POAM II 

measured stratospheric profiles of ozone and NO2, and POAM III added H2O profiles [Lumpe et 

al., 2006]. The Improved Limb Atmospheric Spectrometer (ILAS) and another TOMS 

instrument were launched into orbit in 1996 by the Japanese Space Agency on its Advanced 

Earth Observing Satellite (ADEOS). A second ILAS instrument began operations from ADEOS 

II in 2002. Atmospheric scientists at University of Wuppertal, Germany, deployed their 

Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument as a 

Shuttle Pallet Satellite (or SPAS) on flights in 1994 and 1997 [Offermann et al., 1999; 

Grossmann, 2000]. CRISTA employed three telescopes pointing at the Earth’s limb and at 

different horizontal angles, in order to provide measurements of a higher spatial density. POAM, 

ILAS, and CRISTA were focused on making measurements of important minor and trace 

stratospheric species, especially at the higher latitudes.
32 

Satellites launched from the Space Shuttle are in slowly precessing orbits and, in the case of 

UARS, required occasional yaw maneuvers to meet their thermal and viewing requirements and 

to maintain proper solar array exposure throughout the year [Reber et al., 1993]. Another 

example of a satellite in a precessing orbit is the Tropical Rainfall Measuring Mission 

(TRMM)—a cooperative venture of the U.S. and Japan and launched by the Japanese Space 

Agency in November 1997. The goal of TRMM was to quantify rainfall amounts and latent 

heat release at low latitudes as a function of the local times associated with convective 

development [Kummerow et al., 1998]. On the other hand, the major goal of NASA’s EOS 

satellite observations was to monitor the global surface and atmospheric environment and to 

relate any changes in their characteristics to natural and/or anthropogenic activities. Indeed, this 

objective strains the capabilities and ingenuity of the satellite remote sensor community. The 

goal of resolving statistically significant variations or trends in a given surface or atmospheric 

parameter across all latitudes meant that the observations must be made from satellites in Sunsynchronous, polar orbits. As a result, the EOS spacecraft sequence of Terra, Aqua, and Aura, 

were launched by Atlas or Delta rockets from Vandenberg Air Force Base in California.
33 

7 An Earth Observing System (EOS) plus international contributions (1997-2010)

Selections of the experiments for the three EOS spacecraft were really made in the early 1990s, 

and many of the instruments merely represented refinements of earlier atmospheric sounders and 

Earth imagers. Imaging experiments selected for Terra and Aqua had their heritage based on 

similar instruments on Nimbus and Landsat, and on NOAA’s Advanced Very High Resolution 

Radiometer (AVHRR). NASA had also gained quite a bit of experience for the selections for 

Aura, as a result of the testing and deployment of the engineering or preflight instrument models 

and algorithms for UARS. Members of the several EOS advisory panels were briefed on the 

expected performance of the various instruments proposed for EOS, and they provided 

recommendations to NASA. Algorithms for the creation of the EOS datasets were reviewed and 

made available in Algorithm Theoretical Basis Documents (ATBD) prior to launch, and the 

science teams associated with the experiments were urged to provide their data and report on 

preliminary results shortly after launch. This approach was certainly different from the 

traditional role of a Science Team, as led by a Principal Investigator. One caveat for NASA’s 

vision of multiple copies of each EOS instrument was the subsequent realization that significant 

technology improvements would become available and ought to be incorporated into any followon versions of the instruments. 

The EOS “flagship” spacecraft Terra was launched in December 1999 into a late morning orbit, 

and it carried two instruments for sounding the troposphere—Goddard’s Moderate-resolution 

Imaging Spectroradiometer (MODIS) [King et al., 2003] and the Measurement of Pollution in 

the Troposphere (MOPITT) of University of Toronto, Canada [Liu et al., 2005]. MODIS 

continues to provide, near global-scale information on temperature, precipitable water, clouds, 

and aerosols in the troposphere some ten years after launch. MOPITT is providing distributions 

of tropospheric CO using the pressure modulation or length modulation, gas filter correlation 

approach [Drummond et al., 2010]. Rodgers and Connor [2003] conducted an initial validation 

of CO from MOPITT using an optimal estimation approach to account for the information 

content of its measurements, and they found good agreement for the CO from MOPITT and from 

a ground-based FTIR measurement. EOS Aqua was launched in May, 2002, into an afternoon 

orbit, and it carried a second MODIS instrument plus JPL’s cross-track scanning, grating 

spectrometer AIRS. The AIRS instrument measures tropospheric CO, CH4, CO2, O3, H2O, and 

volcanic levels of SO2. As an example of its capabilities, McMillan et al. [2005] showed daily, 

global maps of CO from AIRS and their excellent correlations with biomass burning activity. 

Recent work of the AIRS experiment team has been focused on retrievals of O3 and CO2. The 

third EOS satellite, Aura, was launched in July, 2004, and it carried two stratospheric 

instruments—a second-generation MLS from JPL and the High Resolution Dynamics Limb 

Sounder (HIRDLS with PIs John Barnett and John Gille) of the University of Oxford and NCAR 

[Taylor, 2011]. An Ozone Monitoring Instrument (OMI with PI Pieternel Levelt) of the 

Netherlands and the Tropospheric Emission Spectrometer (TES with PI Reinhard Beer) of JPL 

round out the Aura payload. The Aura satellite is also in an afternoon orbit along with Aqua and 

several other satellites. They are flying in a formation that has been dubbed as the “afternoon or 

A-Train”. 
34 

At this point it is noted that RMOP Panel member, H. G. Reichle, Jr., of Langley, also proposed 

his MAPS experiment for Terra, but that MOPITT was selected instead. Nevertheless, Reichle 

assisted the MOPITT team by providing them with his datasets on CO and details about the 

characteristics of the MAPS instrument. He later made modifications to the MAPS instrument 

and obtained improved results for retrievals of mid-tropospheric CO from two flights of MAPS 

on Shuttle in 1994 [Reichle et al., 1999]. He and his colleagues at Langley also participated in a 

joint U.S./Russian activity in 1997 to install the MAPS instrument on the orbiting space station, 

MIR. But because of a collision of a supply vehicle during its docking attempt with MIR, the 

planned operations of MAPS from MIR were never carried out. Several years later MIR was deorbited with MAPS aboard, and no backup instrument remained for another flight opportunity. 

RMOP Panel member, James Russell, III, also proposed the experiment Spectroscopy of the 

Atmosphere using Far Infrared Emission (SAFIRE), but a second-generation of the JPL MLS

experiment was chosen for EOS Aura. Langley’s only successful contribution to the suite of 

EOS satellite payloads was SAGE III. It was launched aboard a Russian Meteor-3M satellite in 

December 2001 and represented a continuation of the earlier SAGE experiments by Pat 

McCormick. SAGE III obtained measurements by both solar and lunar occultation for nearly 4 

years and was focused on species and processes associated with ozone at polar latitudes. 

Technological advances, such as Charge Coupled Device (CCD) linear array detectors, were also 

employed for obtaining the profile measurements from SAGE III [Wang et al., 2006]. 

Atmospheric instruments on the EOS payloads were designed to obtain temperature and/or 

species profile or column information with adequate S/N (and accuracies) and improved vertical 

resolutions, where possible. MLS continues its excellent performance for the monitoring of 

ozone and its related species from the upper troposphere and well into the mesosphere. In 

addition, Aura MLS provides profile information about stratospheric OH using a 2250 GHz

receiver. The OMI instrument succeeds TOMS in continuing the monitoring of total ozone on 

the global scale [Levelt et al., 2006]. OMI is also providing estimates of column NO2 and 

bromine oxide (BrO), although Salawitch et al. [2010] cautioned that sometimes part of the BrO 

column must be attributed to its partial column amounts of the lower stratosphere. TES, along 

with GOME-2, MOPITT, and AIRS is providing new information on regional-scale pollutant 

molecules and their relation to industrial and biomass burning sources. In particular, TES is 

obtaining good estimates of ozone in the upper versus the lower troposphere in regions of 

biomass burning [Jourdain et al., 2007]. Finally, despite the unfortunate, partial restriction of its

view of the horizon, HIRDLS is delivering good quality, high vertical resolution profiles of a 

number of species in the stratosphere, at least down to the tops of clouds [Gille et al., 2008]. 

HIRDLS represents a significant advance over earlier infrared limb sounders. It contains four 

CO2 and three O3 radiometer channels, in order to provide a more linear response between 

changes in the radiances with altitude. HIRDLS is providing retrieved temperature and ozone 

profiles throughout the stratosphere and with vertical resolutions of better than 2 km. The 

relatively narrow spectral widths and vertical dimensions for its channels required the use of 

cooled, low noise detectors. Pressure-modulated gas cells were not used for the HIRDLS 

instrument. Thus, S/N for the radiance profiles of HIRDLS is improved over that of ISAMS. 
35 

In the 1990s NASA’s Earth observing activities fully considered the associated contributions of 

other nations—Japan, Canada, Russia, and the European Union. They were beginning to deploy 

their own enhanced satellite measurement capabilities. The European Space Agency launched

an environmental satellite (ENVISAT) into orbit in 2002, and it carried three experiments 

focused on measurements from the upper stratosphere to the lower mesosphere. They are the

relatively, high spectral resolution, limb emission experiment Michelson Interferometer for 

Passive Atmospheric Sounding (MIPAS), the Global Ozone Monitoring by Occultation of Stars 

(GOMOS), and the (SCanning Imaging Absorption SpectroMeter for Atmospheric 

CartograpHY) or SCIAMACHY. MIPAS resolves molecular spectra and provides information 

about isotopic species as well as emissions from vibrationally-excited molecular transitions 

[Fischer and Oelhaf, 1996]. As such, its measurements are being used to determine the sources 

of the observed atmospheric radiances. Wargan et al. [2005] showed that the higher accuracy of 

the MIPAS ozone leads to a substantial improvement in model assimilated ozone below the 

ozone maximum, compared with that from SBUV. The Canadian Space Agency launched a 

SCIence SATellite (SCISAT) on a Pegasus XL vehicle from Vandenberg AFB in 2003 with 

funding from NASA. SCISAT carried a second-generation ATMOS instrument or the 

Atmospheric Chemistry Experiment (ACE) into near polar orbit for the observation of chemical 

species in the middle atmosphere via solar occultation [Bernath et al., 2005]. SCISAT carries a 

second occultation instrument, Measurements of Aerosol Extinction in the Stratosphere and 

Troposphere Retrieved by Occultation (MAESTRO), that has been used successfully to obtain 

profiles of water vapor in the upper troposphere/lower stratosphere (UT/LS) [Sioris et al., 2010]. 

Canadian researchers also teamed with those from Finland, France, and Sweden on the launch of 

the Swedish satellite ODIN in 2001. It consisted of a sub-millimetre radiometer (SMR) and the 

Optical Spectrograph and Infrared Imaging System (OSIRIS), the latter functioning essentially as 

a limb-scattering instrument. In general, POAM, GOMOS, ACE, OSIRIS, and SAGE III were

focused on obtaining an improved understanding of the processes affecting the distributions of 

polar ozone. Further tests of limb scattering techniques are being conducted using data from 

OSIRIS and SCIAMACHY in the manner of the Shuttle Ozone Limb Sounding 

Experiment/Limb Ozone Retrieval Experiment (or SOLSE/LORE) of 1997, as analyzed by 

Flittner et al. [2000] and McPeters et al. [2000]. 

NASA’s Office of Space Science launched the Thermosphere Ionosphere Mesosphere Energetics 

and Dynamics (TIMED) satellite in December 2001. TIMED carried four experiments, 

including the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). 

SABER provides near global-scale temperature and ozone, and nitric oxide (NO) radiance

profiles, among other parameters. Together, the radiances from these three species are being 

used to characterize the energy balance of the mesosphere and lower thermosphere. It is 

noteworthy that the genesis of the SABER experiment dates back to the SPIRE measurements of 

1977 by AFGL. The SABER concept was initially proposed by RMOP Panel member, James 

Russell III, in 1977 or during the time frame of the middle atmosphere experiments of Nimbus 6 

and 7. However, the selection of SABER for TIMED did not occur until 1993. Thus, the 

SABER instrument team was able to incorporate a number of improvements for its onboard 

cooler and detectors during the intervening years [Russell et al., 1999]. The inclusion of the 

effects of line mixing for the strong-line, 15-μm region of CO2 led to improved accuracies for the 
36 

forward radiance model in the SABER local thermodynamic equilibrium (LTE) algorithm for 

T(p) in the stratosphere and lower mesosphere. That model also provides a more accurate 

registration of the radiance profiles with pressure for all the retrieved species profiles, as 

indicated with comparisons of the SABER T(z) with those from the Rayleigh and Na lidar 

measurements and from the MIPAS data [Remsberg et al., 2008]. Chris Mertens of GATS, Inc., 

and later of Langley, developed the non-LTE forward models for the T(p) retrievals and for the 

observed CO2 radiances from the mesosphere and lower thermosphere [Mertens et al., 2001]. 

Marty Mlynczak supplied the non-LTE algorithm for retrievals of ozone profiles from the 9.6-

μm radiances and also an algorithm for deriving ozone from the O2(

1

D) radiances [Mlynczak et 

al., 2007]. 

 

Satellite measurements of OH fluorescence at 309 nm were conducted by NRL with its Spatial 

Heterodyne Imager for Mesospheric Radicals (SHIMMER) from March 2007 to October 2009 

[Englert et al., 2010]. SHIMMER OH values are in agreement with those from Aura MLS and 

with a standard photochemical model from 60 to 80 km, resolving a long-standing discrepancy 

about the chemical effects of HOx radicals on ozone. The SHIMMER instrument also 

demonstrates the many technological advancements for middle ultraviolet measurements since 

the time of the Javelin rocket test measurements of the horizon made from Wallops Island in 

1961 [McKee et al., 1964]. Steady increases of atmospheric CO2 have led to a cooling of the 

upper atmosphere and a contraction of thermospheric densities, as determined by Langley 

researchers from satellite drag measurements over many years [Keating et al., 2000]. The Solar 

Occultation for Ice Experiment (SOFIE) instrument was launched in April 2007 on the 

Aeronomy of Ice in the Mesosphere (AIM) spacecraft by a Pegasus vehicle from Vandenberg 

AFB. James Russell, III, of Hampton University is the Principal Investigator of this NASA 

Small Explorer (SMEX) satellite mission. The SOFIE instrument concept is a direct outgrowth 

of the design of HALOE on UARS [Gordley et al., 2009a]. SOFIE data are being used to look 

for evidence of trends in temperature and species near the summer mesopause. Such occultation 

experiments are especially suitable for studies of global atmospheric change, as envisioned by 

the members of the Gas Species Panel of the RMOP Workshop. 
37 

8 Joint Polar Satellite System (JPSS) and future sensing prospects

Since the early days of weather forecasting, it has always been clear that good measurements of 

the temperature and moisture profiles are needed as input to the models in order to maintain 

some skill in their predictions out to 5 or 7 days. On the other hand, the goal of monitoring the 

atmosphere for its climate-related changes requires accurate, long-term measurements of the 

radiatively-active constituents of CO2 (or temperature), H2O, and O3. Satellite measurements of 

the air quality must be made on urban to regional scales, in order to link pollutants to their 

sources. Thus, in many respects the observational goals for weather, climate, and air quality are 

incompatible and difficult to achieve with single satellites, such as EOS, ENVISAT, or MetOp. 

The next-generation sensors for the U. S. operational satellite system JPSS were selected in the 

early 1990s, based on an updated set of measurement goals and environmental data records 

(EDRs) for its temperature sounder and imager and for its ozone measuring instrument (the 

Ozone Mapping and Profiler Suite or OMPS). The temperature sounder combines a cross-track 

infrared sounder (CrIS) with an Advanced Technology Microwave Sounder (ATMS). The JPSS 

Visible/Infrared Imager Radiometer Suite (or VIIRS) has its heritage from EOS MODIS and the 

previously operational AVHRR sensor of NOAA. OMPS has its heritage from TOMS or OMI 

plus SBUV, although NOAA’s technical advisory panel report of 1995 recognized that an 

SBUV-type sensor cannot provide ozone with vertical resolutions of any better than 6 to 8 km. 

Nevertheless, it is hoped that the ozone EDR of 3 to 5 km vertical resolution can be obtained for 

the lower stratosphere using a limb-scattering algorithm. NASA intends to demonstrate the 

capabilities of all these sensors on its National Polar-orbiting Operational Environmental 

Satellite System (or NPOESS) Preparatory Project (NPP) satellite in 2011. In this regard, NPP 

should also be considered as another in the long series of NASA research satellites. 

A major goal of the NPP sensors is to be able to obtain climate quality measurements of 

stratospheric ozone, plus the tropospheric moisture and temperature profiles for weather forecast 

models. It is expected that the relevant sensors will benefit from the improved on-board 

calibrations and better spatial resolutions of their measurements. William Smith, Sr., of Langley 

and now of Hampton University also proposed his Geostationary Imaging Fourier Transform 

Spectrometer (GIFTS) instrument for a flight opportunity, but its demonstration was secondary 

to the NASA evaluation of the sensors on NPP. Nevertheless, Smith along with Xu Liu, Dan 

Zhou, and Allen Larar of Langley are applying their algorithms for the efficient use of

hyperspectral measurements from the sounders and imagers on the MetOp satellite [Liu et al., 

2006], and they are preparing to evaluate similar spectral measurements from CrIS on NPP. 

David Flittner and Didier Rault of Langley have developed limb-scatter algorithms that can be 

used for retrievals of ozone in the lower stratosphere with a vertical resolution of order 3 km. 

The NASA Science Mission Directorate (SMD) now follows a blueprint for its Earth Science 

satellite observation program based on a Decadal Survey document prepared by the National 

Research Council [NRC, 2007]. The Orbiting Carbon Observatory (OCO) satellite is part of that 
38 

strategy. OCO is designed to measure and map column CO2 amounts in the lower troposphere 

and hopefully to link any elevated amounts to their source regions. A feasibility test of the OCO 

concept was performed using near infrared measurements of CO2 at 1.6 μm from spectral 

measurements of the SCIAMACHY experiment on ENVISAT, and the results are promising 

[Boesch et al., 2006]. NASA launched OCO in 2009, but it failed to achieve orbit. An OCO-2 

instrument is being readied for a launch opportunity in 2013. In a parallel effort the Japanese 

Space Agency launched its Greenhouse gases Observing Satellite (GOSAT) in January 2009, 

and they are obtaining useful measurements of CO2 and CH4 from Earth orbit [Butz et al., 2010]. 

NASA’s Decadal Survey missions are segmented into Tier 1, Tier 2, and Tier 3 experiment 

payloads, and the Tier 1 experiments have been named. The Climate Absolute Radiance and 

Refractivity Observatory (CLARREO) Project at Langley is one of those Tier 1 experiments. An 

important resource and motivator for the members of the RMOP Panel of 1971 was Richard 

Goody of Harvard University. Most recently, he and his colleagues advocated for the monitoring 

of Earth’s climate from satellites, and their vision was included as part of CLARREO [Goody et 

al., 2002]. CLARREO is being designed to achieve the longer-term spectral radiance 

measurements that are necessary for an improved understanding of Earth’s climate [Huang et al., 

2010; Sandford et al., 2010]. In fact, atmospheric survey measurements with the proposed 

infrared spectrometer of CLARREO are very reminiscent of the SIRS and IRIS instruments that 

were flown by Wark and Hanel on Nimbus 3 and 4. Furthermore, the observations from the 

GPS/RO satellites of JPL/NSF are already showing that it is possible to achieve profiles of 

temperature and moisture in the troposphere with even better vertical resolutions and accuracies 

then envisioned from infrared sounders. A similar RO sounder is being considered for 

CLARREO, as well. Bruce Wielicki, CLARREO Mission Scientist at Langley, hopes to apply 

better preflight and in-flight calibration methods for its sensors. However, budgetary constraints 

may delay this Tier 1 experiment until after 2020.

Two Tier 2 missions for the study of atmospheric composition are under study at Langley and 

Goddard and another one at JPL. The first effort at Langley is an outgrowth of a 2008 Workshop 

on the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS), and it is a 

concept from Ed Browell. The experiment will make measurements of column CO2 using 

tunable laser sensing technologies from a satellite, hopefully later in the decade. Langley, 

Goddard, and JPL personnel have already been conducting coordinated, airborne tests of laser 

systems operating at the 1.57 and 2.06 μm lines of CO2 for the purpose of demonstrating the 

method, and the initial results are promising. The second Langley/Goddard mission concept is 

called Geostationary Coastal and Air Pollution Events (GeoCAPE). It consists of a gas filter 

correlation radiometer (GFCR) for making measurements at both 2.3 μm and 4.6 μm, in order to 

distinguish amounts of CO in the atmospheric boundary layer. Currently, its technology follows 

from the earlier MAPS concept, and Doreen Neil is the Langley instrument scientist. GeoCAPE 

is also being designed to carry a high spatial resolution, hyperspectral spectrometer that will 

operate in the uv and visible region, as well as an imaging spectrometer; Scott Janz of Goddard is 

the instrument scientist for the high spatial resolution experiment. All three instruments would 

make measurements from geostationary orbit, in order to monitor regional-scale pollutants and 
39 

the ecology of coastal zones over relatively short time intervals. The Tier 2 experiment from 

JPL is labeled a hyperspectral infrared imager (HyspIRI) and is being designed to operate from 

low Earth orbit. All the Tier 2 mission concepts are in their Pre-phase A study period. 

Tropospheric measurements of CO are being made with MOPITT on EOS Terra [Drummond et 

al., 2010], but its measurements of column CO and CH4 are limited to some extent by the small 

amount of thermal contrast between the surface and the top of boundary layer. The solar 

backscatter measurements of column CO by MOPITT are affected by the natural variations of 

the surface albedo in the short time that it takes for the chopper to switch between the absorbed 

and non-absorbed channels for the gas filter correlation measurement. Gordley et al. [2009c] 

have devised a Digital Array Gas Radiometer (DAGR) concept that will minimize any 

degradation due to the natural variations of the surface albedo. The DAGR approach could be 

applied to both imager and sounder measurements of gases in the atmospheric boundary layer. 

On the other hand, Schneising et al. [2011] are showing that they are already obtaining 

reasonably accurate column-averaged results for CO2 and CH4 with the spectrally-selective and 

sensitive grating spectrometer, SCIAMACHY. Similar capabilities are being demonstrated with 

the data from the instruments on the Japanese GOSAT.

The international atmospheric science community has also been focused on developing 

chemistry/climate models (CCM) that can predict the changes that one can expect for

stratospheric ozone due to a decrease in ozone-depleting substances (ODS) but modulated by the 

changes from increases in the greenhouse gases (GHG), in particular CO2 and CH4. Model 

simulations have been conducted for the period of 1979 to the present, and the results have been

compared with the satellite temperature and ozone records for verification. In fact, an 

engineering model of SAGE III is being refurbished and tested at Langley in preparation for 

attaching it to the ISS in 2014 for the purpose of adding to the lower stratospheric ozone record. 

An implicit assumption for the ozone analyses is that the models are representing properly all of 

the physical processes that are important at climate time scales. Yet, it is clear that the 

combination of radiosonde data and satellite records are lacking the necessary calibrations for a 

proper verification of the predictions from the same CCMs.

Accurate, long-term observations with high vertical resolutions are also needed to isolate the 

radiative effects of the changing GHG on climate, especially for H2O close to the tropopause 

[Solomon et al., 2010]. It is also critical to be able to differentiate between the long-term 

changes in ozone due to anthropogenic and natural forcings. Solar occultation (SO) provides 

accurate profiles and trends of O3 and H2O in the lower stratosphere and with the necessary 

vertical resolution of at least 2 km [e.g., Gordley et al., 2009b]. One concern about the SO 

technique has been that it does not provide a near-global set of profiles each day. However, 

Remsberg and Lingenfelser [2010] concluded that the SO sampling from SAGE II and HALOE 

was adequate for resolving the seasonal and longer-term variations in stratospheric ozone. They 

also found that the vertical resolution from SO is adequate for separating out the effects on ozone 
40 

of the 11-yr, solar uv-flux forcing from those due to the longer-term changes of the GHG. A 

further important benefit of GPS/RO measurements of temperature in the lower stratosphere and 

of SO measurements of stratospheric ozone and H2O is that it is much easier to obtain good 

calibrations for RO and SO measurements. 
41 

9 Summary

This report provides a brief review of the measurement methods employed at Langley to

characterize the atmospheric environment. Early remote methods include passive sensing of the 

Earth’s horizon and active sensing of atmospheric turbulence. In the early 1970s NASA began 

to emphasize its Earth applications programs and its capabilities for measuring regional to 

global-scale atmospheric pollution from Earth orbit. A workshop (RMOP) was held in 1971 to 

define the environmental problems and the remote sensing techniques that could be applied to 

their study. An RMOP Workshop Report was the outcome, and it represented a blueprint for the 

associated technology developments that would be pursued for the following two decades.

This report is a retrospective account of the developments that led to the successful use of 

satellite sensors for measuring temperature and gaseous species profiles of the atmosphere. 

Researchers at NASA Langley focused their attention on developing atmospheric remote sensors 

based on solar occultation, limb infrared emission, and gas filter correlation radiometry. 

Auxiliary in situ, passive, and active measurement techniques were also developed and operated 

from ground-based, balloon-borne and/or aircraft platforms for the purpose of verifying the 

measurements from the engineering or pre-flight models of the proposed satellite instruments. 

Final selections for a satellite flight opportunity were ultimately based on the scientific goals of 

the experiment and on the demonstrated performance for its instrument. A theme throughout the 

report is the need to obtain good accuracy and precision for the measurements and their retrieved 

quantities, while providing the desired spatial resolutions at the same time.

During the initial two decades following RMOP, candidate technologies were funded through 

NASA’s AAFE Program. Since the mid-1990s sensor developments have been supported from 

NASA’s New Millenium Program (NMP), Instrument Incubator Program (IIP), and the Earth 

System Science Pathfinder (ESSP). Selections for flight opportunities follow the guidelines 

provided by the NRC in 2007 as part of NASA’s Decadal Plan for the Earth Sciences. It is 

emphasized that many of the candidate instrument concepts of today still rely on the proof-ofconcept, sensor demonstration approaches that Morris Tepper, Don Lawrence, Jr., William 

Kellogg, and the members of his RMOP subpanel asked for in their report of 1971. Langley and 

NASA continue to develop new instruments based on this long heritage of making remote 

measurements of the atmosphere (also see Remsberg et al. [2011]). 

Acknowledgements. EER developed this historical retrospective as a Distinguished Research 

Associate at Langley, administered by Dennis Bushnell. EER was supported by Gary Gibson, 

Malcolm Ko, Pamela Rinsland, and Lelia Vann in this activity. Richard Davis introduced him to 

the early reports from Project Scanner, and Harvey Melfi recounted for him the development of 

lidar sensing in the 1960s. EER coordinated his findings with those of Lou Smith, who has 

assembled a similar retrospective on satellite radiation budget measurements by Langley. EER 

recognizes Sam Katzoff, Editor of the RMOP Report; he died in 2010 at the age of 101. 
42 

Appendix A

Acronyms:

AAFE Advanced Applications Flight Experiments 

ACE Atmospheric Chemistry Experiment

ADEOS ADvanced Earth Observing Satellite

AEM Atmospheric Explorer Mission 

AESA Atmospheric Effects of Stratospheric Aircraft

AESD Atmospheric Environmental Sciences Division 

AFCRL Air Force Cambridge Research Laboratories

AFGL Air Force Geophysics Laboratories

AIM Aeronomy of Ice in the Mesosphere 

AIRS Atmospheric Infrared Sounder 

AMSU Advanced Microwave Sounding Unit 

ASCENDS Active Sensing of CO2 Emissions over Nights, Days, and Seasons 

ASD Atmospheric Science Division 

ASTP Apollo-Soyuz Test Project

ATBD Algorithm Theoretical Basis Document

ATMOS Atmospheric Trace Molecule Spectroscopy

ATMS Advanced Technology Microwave Sounder 

ATOVS Advanced TOVS 

ATS Advanced Technology Satellite

AVHRR Advanced Very High Resolution Radiometer

BOIC Balloon Ozone Intercomparison Campaign 

BUV Backscatter Ultra-Violet

CAA Clean Air Act
43 

CCD Charge Coupled Device 

CCM Chemistry Climate Model

CFC Chlorofluorocarbon 

CIAP Climatic Impact Assessment Program

CIMATS Correlation Interferometer for the Measurement of Atmospheric Trace Species

CLAES Cryogenic Limb Array Etalon Spectrometer

CLARREO CLimate Absolute Radiance and REfractivity Observatory

COPE Carbon Monoxide Pollution Experiment 

CrIS Cross-track Infrared Sounder 

CRISTA Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere

CWA Clean Water Act

DAGR Digital Array Gas Radiometer

DIAL DIfferential Absorption Lidar 

DOD Department of Defense

DOT Department of Transportation 

 

EDR Environmental Data Record

ENVISAT ENVIronmental SATellite

EOS Earth Observing System

EP Earth Probes 

EPA Environmental Protection Agency 

EQPO Environmental Quality Program Office

ERBS Earth Radiation Budget Satellite

ERS European Remote Sensing 

ESA European Space Agency 

ESMR Electronic Scanning Microwave Radiometer
44 

ESSD Environmental and Space Sciences Division 

ESSP Earth System Science Pathfinder

FID Flight Instruments Division

FTIR Fourier Transform InfraRed

GATS Gordley and Associates Technical Software

GeoCAPE Geostationary Coastal and Air Pollution Events 

GFCR Gas Filter Correlation Radiometer

GHG GreenHouse Gases

GIFTS Geostationary Imaging Fourier Transform Spectrometer

GMCC Geophysical Monitoring for Climate Change 

GOME Global Ozone Monitoring Experiment 

GOMOS Global Ozone Monitoring by Occultation of Stars 

GOSAT Greenhouse gases Observing SATellite

GPS Global Positioning System 

GTE Global Troposphere Experiment 

HALOE HALogen Occultation Experiment

HIRDLS HIgh Resolution Dynamics Limb Sounder 

HIRS High-resolution Infrared Radiation Sounder 

HIS High-resolution Interferometer Sounder 

HITRAN HIgh-resolution TRANsmission

HRC Honeywell Radiation Center 

HSCT High Speed Civil Transport 

HSRP High Speed Research Program

HyspIRI Hyperspectral InfraRed Imager
45 

IASI Infrared Atmospheric Sounding Interferometer 

IIP Instrument Incubator Program 

ILAS Improved Limb Atmospheric Spectrometer 

IRD Instrument Research Division 

IRIS InfraRed Interferometer Spectrometer

ISAMS Improved Stratospheric And Mesospheric Sounder 

ISS International Space Station

ITPR Infrared Temperature Profile Radiometer

JPL Jet Propulsion Laboratory 

JPSS Joint Polar Satellite System

 

LACATE Lower Atmospheric Composition And Temperature Experiment

LaRC Langley Research Center

LIMS Limb Infrared Monitor of the Stratosphere 

LORE Limb Ozone Retrieval Experiment

LRIR Limb Radiance Inversion Radiometer 

LTE Local Thermodynamic Equilibrium

MAESTRO Measurements of Aerosol Extinction in the Stratosphere and Troposphere 

 Retrieved by Occultation

MAPS Measurement of Air Pollution from Satellites

MHS Microwave Humidity Sounder 

MIPAS Michelson Interferometer for Passive Atmospheric Sounding 

MIT Massachusetts Institute of Technology 

MODIS MODerate-resolution Imaging Spectro-radiometer
46 

MOPITT Measurement Of Pollution In The Troposphere 

MRN Meteorological Rocket Network

MSU Microwave Sounding Unit 

NACA National Advisory Committee for Aeronautics

NAS National Academy of Sciences 

NASA National Aeronautics and Space Administration

NCAR National Center for Atmospheric Research

NDACC Network for the Detection of Atmospheric Composition Change 

NEMS Nimbus E Microwave Spectrometer

NESS National Environmental Satellite Service

NMP New Millenium Program

NRL Naval Research Laboratory

NOAA National Oceanic and Atmospheric Administration

NPOESS National Polar-orbiting Operational Environmental Satellite System

NPP NPOESS Preparatory Project

NRC National Research Council

 

OA Office of Applications

OAO Orbiting Astronomical Observatory 

OAST Office of Aeronautics and Space Technology

OCO Orbiting Carbon Observatory 

ODS Ozone Depleting Substances 

OMI Ozone Monitoring Instrument 

OMPS Ozone Mapping and Profiler Suite

OSIRIS Optical Spectrograph and InfraRed Imaging System

OSTA Office of Space and Terrestrial Applications
47 

PAN Peroxy-Acetyl Nitrate

PMR Pressure Modulator Radiometer

POAM Polar Ozone and Aerosol Measurement

RMOP Remote Measurement Of Pollution 

RO Radio Occultation

RMS Root-Mean-Square 

SABER Sounding of the Atmosphere using Broadband Emission Radiometry 

SAFIRE Spectroscopy of the Atmosphere using Far InfraRed Emission 

SAGE Stratospheric Aerosol and Gas Experiment 

SAIC Science Applications International Corporation 

SAM Stratospheric Aerosol Monitor 

SAMS Stratospheric And Mesospheric Sounder 

SASC Systems and Applied Sciences Corporation 

SBUV Solar Backscatter Ultra-Violet

SCAMS SCAnning Microwave Spectrometer

SCEP Study of Critical Environmental Problems

SCIAMACHY SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY 

SCISAT SCIentific SATellite

SCMR Surface Composition Microwave Radiometer

SCR Selective Chopper Radiometer

SD Science Directorate

SHIMMER Spatial Heterodyne Imager for Mesospheric Radicals on STPSat-1 

SIRS Satellite InfraRed Spectrometer

SMD Science Mission Directorate
48 

SME Solar Mesosphere Explorer 

SMEX SMall Explorer

SMIC Study of Man’s Impact on Climate

SMR Sub-Millimeter Radiometer

S/N Signal-to-Noise

SO Solar Occultation

SOFIE Solar Occultation For Ice Experiment

SOLSE Shuttle Ozone Limb Sounding Experiment 

SPAS Shuttle PAllet Satellite

SPIRE SPectral Infrared Rocket Experiment

SSBUV Shuttle SBUV

SST SuperSonic Transport 

SSU Stratospheric Sounding Unit 

STC Science and Technology Corporation 

SUNY State University of New York

TES Tropospheric Emission Spectrometer 

THIR Temperature Humidity Infrared Radiometer

TIMED Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics

TIROS Television InfraRed Observation Satellite

TOMS Total Ozone Mapping Spectrometer 

TOR Tropospheric Ozone Residual 

TOVS TIROS Operational Vertical Sounder

TRMM Tropical Rainfall Measuring Mission

UARP Upper Atmosphere Research Program

UARS Upper Atmosphere Research Satellite
49 

UT/LS Upper Troposphere/Lower Stratosphere 

VIIRS Visible/Infrared Imager Radiometer Suite

WMO World Meteorological Organization 
50 

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Remote Measurement of Pollution - A 40-Year Langley Retrospective:

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The National Aeronautics and Space Administration (NASA) phased down its Apollo Moon Program after 1970 in favor of a partly reusable Space Shuttle 

vehicle that could be used to construct and supply a manned, Earth-orbiting Space Station. Applications programs were emphasized in response to the growing 

public concern about Earth's finite natural resources and the degradation of its environment. Shortly thereafter, a workshop was convened in Norfolk,

Virginia, on Remote Measurement of Pollution (or RMOP), and its findings are in a NASA Special Publication (NASA SP-285). The three primary workshop 

panels and their chairmen were focused on trace gas species (Will Kellogg), atmospheric particulates or aerosols (Verner Suomi), and water pollution (Gifford 

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from an Earth-orbiting satellite. The findings and recommendations of the RMOP Report represent the genesis of and a blueprint for the satellite, atmospheric 

sensing programs within NASA for nearly two decades. This paper is a brief, 40-year retrospective of those instrument developments that were an outgrowth 

of the RMOP activity. Its focus is on satellite measurement capabilities for temperature and gaseous species that were demonstrated by atmospheric 

technologists at the Langley Research Center. Limb absorption by solar occultation, limb infrared radiometry, and gas filter correlation radiometry techniques 

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Remote sensing; Satellite; Pollution; Species; Temperature

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