Aircraft Laser Infrared Absorption Spectrometer (ALIAS)

![](media/image1.wmf)Christopher R. Webster (PI), Greg J. Flesch, Katy
Modarress,

Jess Landeros, Lance Christensen

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1.  "Quantum cascade laser measurements of stratospheric methane (CH~4~)
    and nitrous oxide (N~2~O)", C.R. Webster, G.J. Flesch, D.C.
    Scott, J. Swanson, R.D. May, W.S. Woodward, C. Gmachl, F. Capasso,
    D.L. Sivco, J.N. Baillargeon, A.L. Hutchinson, A.Y. Cho, *Applied
    Optics*, *[40]{.underline}*, 321-326, 2001.

2.  \"Aircraft (ER-2) Laser IR Absorption Spectrometer (ALIAS) for
    In-situ Stratospheric Measurements of HCl, N~2~O, CH~4~, NO~2~, and
    HNO~3~\", C.R. Webster, R.D. May, C.A. Trimble, R.G. Chave and J.
    Kendall, *Appl. Optics, [33]{.underline}*, 454-472, 1994.

**Airborne Laser IR Absorption Spectrometer (ALIAS-II)**

## C.R. Webster (PI), G.J. Flesch, R. Howe, J. Landeros, and L. Christensen

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1\. "Airborne Laser Infrared Absorption Spectrometer (ALIAS-II) for *in
situ* stratospheric measurements of N~2~O, CH~4~, CO, HCl, and NO~2~",

DC Scott, RL Herman, CR Webster, RD May, GJ Flesch, in preparation for
*Applied Optics*, 1998.

2\. "Tropical Entrainment Time Scales Inferred from Strat. N~2~O and
CH~4~ observations", RL Herman, DC Scott, CR Webster, RD May,

> EJ Moyer, RJ Salawitch, YL Yung, GC Toon, B Sen, JJ Margitan, KH
> Rosenlof, HA Michelsen, JW Elkins, *Geophys. Res. Letters*,
> **[25]{.underline}** , 2781-2784, 1998.

**Aircraft Laser Isotope Spectrometer (ALIS) for *in situ* measurements
of ^13^CO~2~, OC^18^O and ^12^CO~2~**

## C.R. Webster (PI) and L. Christensen

Isotopic CO~2~ measurements have also been identified as an important
component of NASA's Earth Science Enterprise's Carbon Cycle Initiative
as part of its program in global climate change. The isotopic
composition of atmospheric CO~2~, and especially its ^13^CO~2~/
^12^CO~2~ ratio, is an established tool for understanding the details of
the global carbon cycle, since this ratio can distinguish between
oceanic and terrestrial biospheric sinks of CO~2~. **During flights of
the DC-8 for validation of the IIP Laser Absorption Spectrometer (LAS)
for global CO~2~ (PI Menzies), ALIS will make the first *in situ*
measurements of ^13^CO~2~ , OC^18^O, and ^12^CO~2~ across the
tropopause.**

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Time series showing the relationship between atmospheric CO~2~ and its
isotopes in the marine boundary layer, made by NOAA CMDL and UC INSTARR.
Greater seasonal variation is seen for the northern high latitudes
driven by the terrestrial biosphere.

Measuring ^13^CO~2~/CO~2~ is not easy, since a precision of better than
1 per mil is required (better than 0.1 per mil desired) to distinguish
trends, seasonal, diurnal, and latitudinal variations. This capability
has never been demonstrated for in-flight atmospheric measurements, but
would have an enormous impact on global carbon science.

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**Figure.** Synthetic spectral region where ALIS will make
^13^CO~2~/^12^CO~2~ isotope measurement demonstration, and schematic of
laser isotope spectrometer optical head. The calibration standard gas
channel "breathes" with the external pressure changes, and both cal gas
and measurement channel are isothermal.

> **JPL Laser Hygrometer for the ER-2 and WB-57F Aircraft**

#### R.L. Herman (PI) and R.D. May (consultant)

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  ![](media/image17.png){width="7.3in" height="4.197222222222222in"}μm.
  The spectrometer features an open-path, multipass (Herriott) cell for
  true in situ monitoring of H2O concentrations with precision levels
  exceeding those of Lyman-α and frost-point hygrometers. External
  sampling outside the aircraft boundary layer minimizes ambiguities.
  Measurement precision is ±0.05 ppmv in the stratosphere for a 2 s
  measurement integration period. The flight-ready instrument weight is
  18 lbs., and power consumption, exclusive of structural heaters, is 7.5
  Watts. The picture below shows the ER-2 instrument as mounted on the
  right-hand super pod for the POLARIS and SOLVE missions. This same
  instrument was flown on the NASA WB-57 as part of WAM (WB-57 Aerosol
  Mission) during April 1998, mounted on an underwing hatch on the right
  wing of the aircraft.

  -----------------------------------------------------------------------

![](media/image18.jpeg){width="6.6819444444444445in"
height="1.413888888888889in"}Open-path, Near-IR Tunable Diode Laser
Spectrometer for Atmospheric Measurements of H~2~O", R.D. May, Journal
of Geophysical Research, Vol 103, No. D15, pp 19161-19172, August
20,1998.

### JPL Near Infrared Laser Hygrometer for the DC-8 Aircraft

R.L. Herman (PI) and R.D. May (consultant)

The DC-8 version of the laser hygrometer is shown here mounted on a
window blank of the DC-8 at fuselage station 490 right.  The optical
path is 50 cm and is a \"there and back\" double pass arrangement.  The
upper blue housing holds the laser and detector, and the lower piece
holds a single 0.5\" diameter mirror for returning the beam to the
detector.  Both the laser and detector are mounted on a single Al disk
that is stabilized in temperature using a thermoelectric cooler (which
actually operates as a heater most of the time during flights).

This instrument has participated in SOLVE and CAMEX-3, and is currently
(August 2001) mounted on the DC-8 as part of the Convection and Moisture
Experiment (CAMEX-4) where flights are underway in Florida.

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"Open-path, Near-IR Tunable Diode Laser Spectrometer for Atmospheric
Measurements of H~2~O", R.D. May, *Journal of Geophysical Research*,
**[103]{.underline}**, 19161-19172, 1998.

**Atmospheric Water & Climate Change: a proposed UAV Science
Demonstration**

Christopher R. Webster (PI), Denise E. Hagan, Robert L. Herman, Michael
J. Mahoney, Ross J. Salawitch, David C. Scott, and Yuk L. Yung

The tiny amounts of water in the upper troposphere and lower
stratosphere have enormous impact on the Earth's climate, driving both
radiative transfer and atmospheric chemistry. We propose to investigate
the processes that are responsible for controlling water vapor
concentrations in the upper troposphere and lower stratosphere through a
series of flight measurements using a suite of already developed and
built aircraft instruments. Our UAV science demonstration will produce
unique measurements not made by conventional platforms, yet will
minimize risk and cost by use of a small suite of existing instruments
including a laser hygrometer, a microwave temperature profiler, solar
radiometers, and a laser spectrometer specifically developed and built
for UAV application. No instrument development is proposed. Our primary
measurements will be those of HDO, H~2~O, CH~4~, N~2~O, CO, temperature
profiles, and solar flux radiometry. Our chosen UAV platform is
AeroVironment's solar powered aircraft, using flights of Helios (test
flights) and Pathfinder Plus that provide cross-tropopause and vertical
profiling ability important to our science demonstration. In addition,
we also propose to include validation measurements of H~2~O and
temperature profiles for either or both of the satellite instruments
AIRS and SAGE III during measurement coincidences, and thereby further
demonstrate the utility of UAVs for satellite validation.

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####### Near-IR Laser Absorption Spectrometer for Global Mapping of CO~2~ in the Lower and Middle Troposphere

JPL: Robert T. Menzies (PI), C.R. Webster, David Tratt, Gary Spiers

Colorado State Univ.: Graeme Stevens

Coherent Technologies: Mark Philips

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-   Near-nadir cw laser (rare-Earth ion doped) illumination of Earth's
    surface from orbit.

-   Analysis of integrated path differential absorption at selected
    transmit frequencies within CO~2~ absorption region to retrieve
    tropospheric CO~2~ profiles.

-   Retrieval of CO~2~ profiles in lower and middle troposphere by
    differential absorption in column above land or ocean backscattering
    surface.

-   Need column to 1-2 ppmv (0.3%) to define spatial gradients.

-   Code Y (IIP) has funded DC-8 aircraft demonstration (2003).

Two near-IR regions selected as suitable for satellite measurements of
global CO~2~ column:

-   1.57 micron band

-   2.05 micron band

-   Optimal combination of optical depth, insensitivity to temperature,
    and few interferences.

**H~2~^18^O Near-IR Tunable Diode Laser Paleothermometer for Determining
Climate Change on Earth and Mars**

## C.R. Webster (PI), G.J. Flesch, M. Hecht and F. Carsey

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We have designed and built a miniature near-IR tunable diode laser
spectrometer for measuring *in situ* the isotopic fractionation
delta-^18^O in water samples from ice cores of either Earth or Mars. The
H~2~^18^O/ H~2~^16^O laser paleothermometer uses a
thermoelectrically-cooled single-mode DFB tunable diode laser (TDL) in
the near-IR region at 1.88 μm to scan over selected vibration-rotation
lines of H~2~^18^O and H~2~^16^O. A working prototype weighing only 220
g has been built with electronics based on the Motorolla HC-12
microcontroller, and has been used to generate spectra whose analysis
demonstrates sensitivities of delta-^18^O of 0.2 per mil precision and 1
per mil absolute accuracy.

####### Water Isotope Spectrometer (WISP)

####### for the Pathfinder/Centurion Solar Electric Aircraft

##### E.J. Moyer, C.R. Webster, D.C. Scott, G.J. Flesch

The WISP instrument inherits much of its design from the ALIAS-II
open-path laser spectrometer. Although built for the WB-57F aircraft,
and flown without laser sources during a single flight of the ACCENT
mission, the WISP Herriott cell has never been tested in the lab or
flight.

![](media/image25.jpeg){width="3.045138888888889in"
height="4.1in"}Measurements of the isotopic composition of atmospheric
water vapor are a critical tool for diagnosing sources of upper
tropospheric humidity and processes of troposphere-stratosphere
exchange. WISP (Water Isotope Spectrometer) is a two-channel tunable
diode laser spectrometer designed for in-situ measurement of the
isotopic composition of water vapor in the upper troposphere and lower
stratosphere. Simultaneous, independent measurements of H~2~O, HDO,
H~2~^17^O, H~2~^18^O and CH~4~ are made by scanning laser light at 1484
and 7299 cm^-1^ (6.74 and 1.37 μm) over closely-spaced absorption
features of the different gases. Laser light is injected into an
open-path multipass Herriott cell for a total pathlength of 100 meters.
The instrument is designed for aircraft platforms, and is intended to
fly on the remotely-piloted, solar-powered aircraft Centurion, operated
by NASA ERAST. Centurion provides long flight durations at upper
tropospheric and stratospheric altitudes, while the extreme slowness of
the aircraft (airspeeds of \~ 40 mph) allows for long integration times
over small spatial regions. The baseline noise on WISP should be
approximately one part in 10^-5^ absorption, providing an instrument
sensitivity for δ^18^O (the ratio of H~2~^18^O to H~2~O, relative to a
standard, in per mil units) of \~ 35 per mil, limited by systematic
errors. Sensitivity for δD is expected to range from \~35 per mil in the
troposphere to 80 per mil in the lower stratosphere, limited by loss of
signal with altitude.

**Balloon-borne Laser In-Situ Spectrometer (BLISS)**

## ![](media/image27.wmf)C.R. Webster (PI) and R.D. May

## Lowered Balloon launch 

## retroreflector 

TDL Spectrum of NO~2~ Diurnal Cycle of NO~2~ at 30 km
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> 1\. \"Balloon Profiles of Stratospheric NO~2~ and HNO~3~ for Testing
> the Heterogeneous Hydrolysis of N~2~O~5~ on Sulfate Aerosols\", C.R.
> Webster, R.D. May, M. Allen, L. Jaeglé, *Geophys. Res. Letters
> [21]{.underline},* 53-56, 1994.
>
> 2\. \"Active Nitrogen Partitioning and the Nighttime Formation of
> N~2~O~5~ in the Stratosphere: Simultaneous In-situ Measurements of NO,
> NO~2~, HNO~3~, O~3~, N~2~O, and jNO~2~ Using the BLISS Diode Laser
> Spectrometer\", C. R. Webster, R. D. May, R. Toumi, and J. Pyle, *J.
> Geophys. Res. [95]{.underline},* 13,851-13,866, (1990)..

#######