BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted SE-590

Summary

The BOREAS RSS-03 team collected multiple remotely sensed data sets from the 
NASA UH-1 helicopter.  This data set includes helicopter-based radiometric 
measurements of forested sites acquired during BOREAS made with an SE-590 
processed to reflectance factors.  The data used in this analysis were collected 
in 1994 during the three BOREAS IFCs at numerous tower and auxiliary sites in 
both the NSA and the SSA.  The 15-degree FOV of the SE-590 yielded a ground 
resolution of approximately 79 m at the 300-m nominal altitude.

Note:  An extensive helicopter log is available for each IFC.  Environmental, 
technical, instrumental, and operational conditions are noted for each 
observation where applicable.  It is strongly recommended that any researcher 
doing extended work with this data set obtain a copy of the helicopter log.

Table of Contents

   *  1 Data Set Overview
   *  2 Investigator(s)
   *  3 Theory of Measurements
   *  4 Equipment
   *  5 Data Acquisition Methods
   *  6 Observations
   *  7 Data Description
   *  8 Data Organization
   *  9 Data Manipulations
   *  10 Errors
   *  11 Notes
   *  12 Application of the Data Set
   *  13 Future Modifications and Plans
   *  14 Software
   *  15 Data Access
   *  16 Output Products and Availability
   *  17 References
   *  18 Glossary of Terms
   *  19 List of Acronyms
   *  20 Document Information

1. Data Set Overview

Radiometer measurements of BOReal Ecosystem-Atmosphere Study (BOREAS) forested 
tower and auxiliary sites were taken from a helicopter platform at nadir.  The 
data were collected in 1994 during the green-up, peak, and senescent stages of 
the growing season at numerous tower and auxiliary sites in both the Northern 
Study Area (NSA) and Southern Study Area (SSA).  The 15-degree field of view 
(FOV) of the Spectron Engineering Spectroradiometer (SE-590) yielded an 
Instantaneous Field of View (IFOV) of approximately 79 m from the 300 m altitude 
typically flown.  The SE-590 has a spectral range of 362.7 to 1122.7 nm, 
although the "usable" SE-590 range is actually ~400 to 900 nm.  The SE-590 
bandwidth is ~15 nm and the spacing between bands ~3 nm.

1.1 Data Set Identification

BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted SE-590

1.2 Data Set Introduction

The helicopter-measured SE-590 radiances and sunphotometer data were used as 
input to Version 4.0 of the Second Simulation of the Satellite Signal in the 
Solar Spectrum (6S) atmospheric correction software to obtain at-surface 
reflectance factors.  The data cover the three Intensive Field Campaign (IFC) 
periods: 31-May through 10-June (IFC-1), 21-July through 8-August (IFC-2), and 
6-September through 16-September (IFC-3). 

1.3 Objective/Purpose

The objective of the study was to acquire multispectral, bidirectional 
reflectance data of the study sites for assessments of spectral, spatial, and 
temporal variability and the impacts of these variabilities on vegetation 
indices.  A helicopter with a pointable stabilized mount was used to carry a 
spectrometer (visible and near-infrared), a spectroradiometer, an infrared 
thermometer, and a video camera.  An auto tracking sunphotometer was also 
deployed to provide data for calculations of irradiance and for atmospheric 
correction of the data.  The latest available version of the 6S atmospheric 
model was used for the calculations of irradiance and for atmospheric 
corrections.

1.4 Summary of Parameters

Helicopter-based measurements of at-helicopter radiances and standard 
deviations, at-helicopter and at-surface (atmospherically corrected) 
reflectances and conditions (surface physical, geometric, and atmospheric) at 
the time of the observation.

1.5 Discussion

These measurements were collected as part of the effort to evaluate models that 
estimate surface biophysical characteristics from remotely measured optical 
signatures.

1.6 Related Data Sets

BOREAS RSS-01 PARABOLA SSA Surface Reflectance and Transmittance Data
BOREAS RSS-02 Level-1b ASAS Imagery: At-sensor Radiance in BSQ Format
BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted Barnes MMR 
BOREAS RSS-03 Atmospheric Measurements from a Helicopter-Mounted Sunphotometer
BOREAS RSS-03 Video Imagery Acquired from a Helicopter Platform
BOREAS RSS-11 Ground Network of Sun Photometer Measurements
BOREAS RSS-12 Automated Ground Sun Photometer Measurements in the SSA
BOREAS RSS-19 1994 Seasonal Understory Reflectance Data
BOREAS RSS-20 POLDER Measurements of Surface BRDF

2. Investigator(s)

2.1 Investigator(s) Name and Title

Dr. Charles L. Walthall, Physical Scientist

2.2 Title of Investigation

Biophysical Significance of Spectral Vegetation Indices in the Boreal Forest

2.3 Contact Information

Contact 1
-------------
Dr. Charles L. Walthall
Physical Scientist
USDA Agricultural Research Service
Remote Sensing and Modeling Laboratory
Beltsville, MD 
(301) 504-6074
(301) 504-5031 (fax)
cwalthal@asrr.arsusda.gov

Contact 2
----------------
Sara Loechel
Faculty Research Assistant
Department of Geography
University of Maryland
Beltsville, MD 
(301) 504-6823
(301) 504-5031 (fax)
sloechel@asrr.arsusda.gov

Contact 3
-------------
Jaime Nickeson
BORIS Team Representative
NASA GSFC
Greenbelt, MD 
(301) 286-3373
(301) 286-0239 (fax)
jaime@ltpmail.gsfc.nasa.gov

3. Theory of Measurements

Radiation striking a vegetative canopy interacts with individual phytoelements 
(leaves, stems, branches) and the underlying substrate.  The interaction depends 
on light quality, radiative form (direct or diffuse), illumination incidence 
angle, vegetative component optical properties, and canopy architecture.  
Radiation is reflected, transmitted or absorbed. 

Reflected radiation measurements were converted to radiances and reflectance 
factor. The reflectance factor is the ratio of the target reflected radiant flux 
to an ideal radiant flux reflected by a Lambertian standard surface irradiated 
in exactly the same way as the target. Reflected radiation from a field 
reference panel corrected for nonperfect reflectance and sun angle was used as 
an estimate of the ideal Lambertian standard surface (Walter-Shea and Biehl, 
1990).

The helicopter missions were designed to provide a rapid means of intensive 
spectral characterization of sites and to provide an intermediate scale of 
sampling between the surface measurements and the higher altitude aircraft and 
spacecraft multispectral imaging devices.  The SE-590 instrumentation was chosen 
to provide compatibility with surface-based radiometers and Thematic Mapper (TM) 
spaceborne sensors.  Off-nadir measurements were made as a means of providing 
more accurate estimates of hemispherical reflectance and for use with 
bidirectional reflectance models.

4. Equipment

4.1 Sensor/Instrument Description

The primary instruments for the BOREAS Remote Sensing Science (RSS)-03 
deployment are the SE-590, a Barnes Modular Multiband Radiometer (MMR), a color 
Charge-Coupled Device (CCD)-based video camera, and a sun-tracking photometer.  
The downward-looking sensor heads, along with a color video camera, are mounted 
on an operator-controlled pointable mount that gives variability in the view 
zenith and view azimuth directions independent of the heading of the aircraft.

The SE-590 is a field portable, microprocessor-controlled spectroradiometer 
developed in the early 1980s.  The sensor is a CCD area array detector with a 
diffraction grating serving as the spectral dispersion component.  The complete 
system consists of a microprocessor-based controller connected by cable to two 
optical cameras containing the sensors.  Lenses are used as collimators for the 
optical cameras.  Although three different optical heads are available for the 
unit, only two can be used at once with a single controller.  The primary unit 
of interest is the visible/near-infrared (VIS/NIR) optical component, which 
employs a silicon sensor and is sensitive to radiation in the 400-nm to 1100-nm 
region.  The short-wave infrared (SWIR) optical camera uses a lead sulfide 
detector with a cooling device for temperature stability and is sensitive to 
radiation in the 1100-nm to 2500-nm spectral region.  Lenses for 1-degree and 
15-degree FOV are available as standard attachments for the VIS/NIR system.  A 
15-degree FOV lens for the SWIR system was specially fabricated for BOREAS.  The 
serial number of the instrument used was 2071.

For the BOREAS deployment, a temperature-controlled box was built to counter the 
effects of ambient temperature on radiometric response of the VIS/NIR optical 
heads.  Two VIS/NIR optical heads were housed in the temperature control box for 
the final configuration, one with a 1-degree FOV lens and one with a 15-degree 
FOV lens.  The SWIR optical head was mounted external to the box with a 15-
degree FOV lens.  The SWIR head was moved outside the temperature control box to 
avoid conflicts between its temperature control system and the system of the 
temperature control box.  The configuration of the system was such that two of 
the three optical heads could be operated at once using a single SE-590 
controller.  The choice of optical heads (two VIS/NIR or one VIS/NIR and the 
SWIR) also required a change in software because the data stream from the SWIR 
optical head is different from that of the VIS/NIR optical heads. 

For helicopter use, the SE-590 is operated in a slave mode by a dedicated PC 
running DOS. The data stream from the SE-590 is communicated via RS-232 cable to 
the computer, where it is stored on a hard disk.  The unit operates on AC power 
available from the aircraft via inverters with self-contained rechargeable 
batteries inside the controller available for backup.  Sensor integration time 
is set automatically via calculations made on a spectral scan prior to each data 
collection scan. 

The data stream from this device includes digital numbers (DNs) for each 
channel, sensor dwell/integration time, date, time, and maximum signal level in 
DNs. The PC software adds an operator-specified header and the SE-590 time is 
replaced with time from the computer's clock as the data are stored.

4.1.1 Collection Environment

In general, the helicopter was flown during relatively clear days when possible. 
Data collection was attempted during conditions of highest possible solar 
elevation.  All observations were attempted from a nadir observation point and 
usually at 300 m above ground level (AGL).  Exceptions are noted in the 
helicopter log. 

4.1.2 Source/Platform

The UH-1 "Huey" series of helicopters has been available as a platform for the 
system in many field campaigns.  The first 10 years of the system development 
and use were with two UH-1B Huey helicopters, while the aircraft used for BOREAS 
was a UH-1H model Huey helicopter. Wallops Flight Facility (WFF) changed to the 
H-model helicopter because of its increased payload capability, the good 
availability of spare parts, and its widespread use by other organizations.  The 
Bell UH-1H "Iroquois" helicopter, call number N415, was built in 1965 and was 
acquired by WFF in 1993.  Upon acquisition, the aircraft was slightly modified 
for use as a scientific platform. 

Helicopter N415 operates with standard or low mount, rear-leaning skids. The 
engine is a Lycoming T53/L13, which provides 1,400 shaft HP with 1,290 
transmission HP. The fuel capacity provides 2.0 hours of flying time with a 20-
minute fuel reserve under normal modes of operation. The addition of an 
auxiliary fuel tank in the port-side door crewman's position provided an 
additional 15 minutes of flight time during BOREAS given optimum flight 
conditions.

The instrument platform controllers, power supplies and data loggers are mounted 
on 54-inch wide, 72-inch-high steel rack mounts fabricated at WFF.  Three racks 
are situated directly in front of the instrument operators.  Seats for the 
instrument operators are located across the front of the transmission and main 
rotor mast housing.  Whenever possible, existing hard points are used for 
attaching hardware both internally and externally.

The weight of the entire helicopter system with full instrumentation, full fuel, 
and crew members was 9,500 lbs.

4.1.3 Source/Platform Mission Objectives

The helicopter missions were designed to provide a rapid means of intensive 
spectral characterization of sites and to provide an intermediate scale of 
sampling between the surface measurements and the higher altitude aircraft and 
spacecraft multispectral imaging devices.  The instruments were chosen to 
provide compatibility with surface-based radiometers and TM spacecraft sensors.  
Off-nadir measurements were made as a means of providing more accurate estimates 
of hemispherical reflectance and for use with bidirectional reflectance models.

4.1.4 Key Variables

Surface reflectance.

4.1.5 Principles of Operation

Computer control of the instruments provides precise, automatic control and 
ensures proper timing of data collection.  The radiometric instruments are 
configured such that all sensors except the photographic camera can be triggered 
near-simultaneously with a single computer keyboard keystroke.  The command sent 
from the keyboard is first sent to the SE-590, then to the A/D systems.  Raw 
data from each of the instruments are displayed via graphics and tabular 
listings on the main computer screen immediately after scanning.  

The system is configured for multiple sensor data collection.  The MMR, SE-590, 
infrared thermometer, autotracking sunphotometer, and video sensor were the 
primary payload during BOREAS.

4.1.6 Sensor/Instrument Measurement Geometry

The National Aeronautics and Space Administration (NASA) Goddard Space Flight 
Center (GSFC)/WFF helicopter-based optical remote sensing system was deployed to 
acquire canopy multispectral data with an SE-590 while hovering approximately 
300 meters AGL (Walthall et al., 1996).  The 15-degree FOV of the SE-590 yielded 
a ground resolution of approximately 79 m at this altitude.

4.1.7 Manufacturer of Sensor/Instrument

SE-590:
Spectron Engineering, Inc.
25 Yuma Court
Denver, CO  80223
(303) 733-1060

4.2 Calibration

4.2.1 Specifications

Spectral Characteristics
SE-590 Range                  362.7 to 1122.7 nm
"Usable" SE-590 Range         ~400 to 900 nm
Bandwidth                     ~15 nm
Spacing between bands         ~3 nm
Filter function               Gaussian (best approximation)
Spectral bands (reported in data set) [nm]:
402.6 405.3 408.0 410.7 413.4 416.1 418.8 421.5 424.2 426.9 429.6
432.3 435.0 437.8 440.5 443.2 446.0 448.7 451.4 454.2 456.9 459.7
462.4 465.2 467.9 470.7 473.4 476.2 479.0 481.8 484.5 487.3 490.1
492.9 495.7 498.5 501.3 504.1 506.9 509.7 512.5 515.3 518.1 520.9
523.7 526.5 529.4 532.2 535.0 537.9 540.7 543.5 546.4 549.2 552.1
554.9 557.8 560.7 563.5 566.4 569.3 572.1 575.0 577.9 580.8 583.7
586.5 589.4 592.3 595.2 598.1 601.0 603.9 606.8 609.8 612.7 615.6
618.5 621.4 624.4 627.3 630.2 633.2 636.1 639.1 642.0 645.0 647.9
650.9 653.8 656.8 659.8 662.7 665.7 668.7 671.6 674.6 677.6 680.6
683.6 686.6 689.6 692.6 695.6 698.6 701.6 704.6 707.6 710.6 713.7
716.7 719.7 722.8 725.8 728.8 731.9 734.9 738.0 741.0 744.1 747.1
750.2 753.2 756.3 759.4 762.4 765.5 768.6 771.7 774.8 777.8 780.9
784.0 787.1 790.2 793.3 796.4 799.5 802.7 805.8 808.9 812.0 815.1
818.3 821.4 824.5 827.7 830.8 834.0 837.1 840.2 843.4 846.6 849.7
852.9 856.0 859.2 862.4 865.6 868.7 871.9 875.1 878.3 881.5 884.7
887.9 891.1 894.3 897.5 900.7

4.2.1.1 Tolerance

None given.

4.2.2 Frequency of Calibration

Radiometric calibration and spectral calibration procedures were performed 
before and after the field season to check for changes in sensor radiometric 
response.  In-field calibration checks were periodically made with a large, 
portable integrating sphere system.  This sphere was used to calibrate the 
airborne instruments on other aircraft and some of the surface-based radiometric 
instrumentation. 

4.2.3 Other Calibration Information

The question of how to calculate reflectance and correct for atmospheric 
influences on airborne data is a challenging issue.  The irradiance solution for 
the NASA GSFC/WFF helicopter system prior to BOREAS used a second set of 
instruments at a centrally located surface-based calibration site.  The 
instruments were positioned to collect data from a white reflectance panel 
(barium sulfate or halon) periodically during the day starting approximately 30 
minutes before take-off and stopping 30 minutes after landing. 

SE-590 coefficients from the second IFC were calculated in the field.  
Conditions did not change much from the beginning of the first IFC until the end 
of the last IFC; thus, any of the calibration files are sufficient.  The table 
of calibration coefficients is output from a software module that supplied 
default wavelengths, instead of the exact wavelengths of this instrument.  In 
practice, they apply to the closest band as given in the SE-590 data set.

---------------------------------------------------------------------------
Wavelength Coefficient (offset of zero) and r2 from regression
---------------------------------------------------------------------------
  WAVE       COEF        r2                   WAVE       COEF        r2
---------------------------------------------------------------------------

  401.5    177.877   0.944291
  404.3    195.617   0.953270
  407.1    212.354   0.959176
  409.9    240.441   0.969660
  412.7    281.806   0.976171
  415.5    329.396   0.983505
  418.3    362.033   0.985738
  421.1    383.876   0.987624
  423.9    406.884   0.989234
  426.7    427.885   0.990205
  429.5    446.648   0.991536
  432.3    454.986   0.992297
  435.1    476.587   0.994173
  438.0    493.344   0.994685
  440.8    511.822   0.995202
  443.6    522.264   0.995745
  446.4    523.222   0.996257
  449.3    519.927   0.996496
  452.1    514.144   0.997100
  454.9    515.135   0.997069
  457.8    507.969   0.997500
  460.6    497.376   0.997683
  463.5    492.863   0.997825
  466.3    492.648   0.997897
  469.2    487.060   0.998084
  472.0    481.766   0.998269
  474.9    478.953   0.998335
  477.7    469.324   0.998460
  480.6    456.215   0.998530
  483.4    447.377   0.998650
  486.3    441.005   0.998666
  489.2    438.226   0.998647
  492.0    441.260   0.998873
  494.9    449.451   0.998914
  497.8    456.074   0.998928
  500.6    459.451   0.999010
  503.5    454.181   0.999101
  506.4    446.948   0.999090
  509.3    440.210   0.999098
  512.2    434.007   0.999064
  515.1    433.951   0.999189
  518.0    434.958   0.999175
  520.8    441.795   0.999182
  523.7    452.507   0.999234
  526.6    461.811   0.999292
  529.5    470.346   0.999288
  532.4    481.618   0.999324
  535.3    485.763   0.999395
  538.3    486.522   0.999378
  541.2    487.035   0.999372
  544.1    481.228   0.999428
  547.0    471.868   0.999408
  549.9    464.951   0.999458
  552.8    456.612   0.999396
  555.8    454.872   0.999417
  558.7    459.347   0.999432
  561.6    467.344   0.999438
  564.5    478.390   0.999478
  567.5    489.023   0.999479
  570.4    496.558   0.999513
  573.3    505.392   0.999555
  576.3    507.749   0.999551
  579.2    504.828   0.999536
  582.2    498.284   0.999541
  585.1    489.910   0.999553
  588.1    480.059   0.999562
  591.0    470.787   0.999550
  594.0    463.137   0.999574
  596.9    457.157   0.999541
  599.9    454.545   0.999552
  602.9    455.709   0.999546
  605.8    458.806   0.999567
  608.8    463.753   0.999581
  611.8    469.958   0.999595
  614.7    477.498   0.999620
  617.7    482.404   0.999643
  620.7    482.992   0.999660
  623.7    480.767   0.999653
  626.7    477.871   0.999653
  629.6    473.047   0.999663
  632.6    464.294   0.999626
  635.6    456.748   0.999657
  638.6    448.964   0.999647
  641.6    442.057   0.999641
  644.6    436.108   0.999634
  647.6    433.334   0.999650
  650.6    426.841   0.999646
  653.6    424.231   0.999654
  656.6    418.953   0.999628
  659.6    417.769   0.999646
  662.6    419.553   0.999671
  665.7    418.793   0.999664
  668.7    418.464   0.999665
  671.7    418.540   0.999691
  674.7    419.266   0.999675
  677.7    414.472   0.999683
  680.8    408.282   0.999666
  683.8    402.339   0.999697
  686.8    394.407   0.999663
  689.9    383.948   0.999669
  692.9    377.904   0.999662
  695.9    371.917   0.999645
  699.0    366.746   0.999641
  702.0    362.821   0.999658
  705.1    364.155   0.999659
  708.1    361.576   0.999668
  711.2    364.754   0.999664
  714.2    370.359   0.999676
  717.3    372.134   0.999673
  720.4    376.100   0.999686
  723.4    381.964   0.999712
  726.5    383.358   0.999717
  729.6    385.283   0.999733
  732.6    387.747   0.999745
  735.7    389.354   0.999746
  738.8    385.004   0.999735
  741.8    379.187   0.999740
  744.9    371.829   0.999722
  748.0    363.352   0.999721
  751.1    354.343   0.999710
  754.2    347.139   0.999680
  757.3    340.538   0.999703
  760.4    336.410   0.999688
  763.5    329.992   0.999674
  766.6    325.867   0.999690
  769.7    319.102   0.999647
  772.8    311.361   0.999645
  775.9    305.954   0.999653
  779.0    299.664   0.999634
  782.1    296.534   0.999644
  785.2    292.414   0.999615
  788.3    288.519   0.999602
  791.4    287.586   0.999618
  794.5    286.344   0.999597
  797.7    284.828   0.999584
  800.8    282.668   0.999593
  803.9    279.686   0.999592
  807.1    277.144   0.999604
  810.2    275.932   0.999587
  813.3    271.085   0.999558
  816.5    266.655   0.999554
  819.6    262.913   0.999582
  822.7    257.784   0.999555
  825.9    250.574   0.999536
  829.0    244.616   0.999500
  832.2    237.477   0.999479
  835.3    228.120   0.999470
  838.5    219.124   0.999430
  841.6    211.521   0.999392
  844.8    204.434   0.999410
  848.0    195.746   0.999362
  851.1    189.681   0.999332
  854.3    187.142   0.999297
  857.5    185.715   0.999299
  860.6    183.007   0.999294
  863.8    181.422   0.999319
  867.0    180.540   0.999299
  870.2    176.893   0.999283
  873.4    171.383   0.999210
  876.5    167.060   0.999245
  879.7    163.815   0.999196
  882.9    160.072   0.999179
  886.1    156.389   0.999145
  889.3    154.292   0.999143
  892.5    151.666   0.999141
  895.7    147.559   0.999065
  898.9    143.946   0.999039
  902.1    138.765   0.998934


5. Data Acquisition Methods

The use of off-the-shelf field instruments aboard airborne platforms is a cost-
effective and efficient approach to assembling a data collection system.  The 
instruments are generally rugged enough for the harsh operating environment of a 
helicopter, provide data comparable to data sets on the surface, and are easy to 
use and versatile during operation.  The system developed jointly at NASA's GSFC 
and WFF uses several widely accepted field-portable radiometric instruments.  
The system is configured such that instruments from other investigators can be 
deployed on the helicopter with little or no interference with the primary 
instrument system.  An autotracking sunphotometer system, developed specifically 
for use on helicopters, is the newest addition to the system.

The NASA GSFC/WFF helicopter-based optical remote sensing system was deployed to 
acquire canopy multispectral data with an SE-590 while hovering approximately 
300 meters AGL (Walthall et al., 1996).  The 15-degree FOV of the SE-590 yielded 
an IFOV at this altitude of approximately 79 m.  Observations were made over 
various tower and auxiliary sites during all three IFCs.

Measurements were collected as conditions permitted during each IFC.  In 
general, the helicopter would hover 1-2 minutes for each observation (consisting 
of an average number of 20-25 scans).

6. Observations

6.1 Data Notes

See Section 6.2.

6.2 Field Notes

An extensive helicopter log is available for each IFC.  Environmental, 
technical, instrumental, and operational conditions are noted for each 
observation where applicable.

7. Data Description

7.1 Spatial Characteristics

7.1.1 Spatial Coverage

The helicopter visited all of the NSA and SSA tower and category-1 auxiliary 
sites.

Each site listed below was observed by this instrument at least once during the 
1994 campaign at BOREAS:

-------------------------------------------------------------------------- 
   Site Id   Operatl  Longitude   Latitude       UTM         UTM      UTM 
              Grid ID                           Easting     Northing   Zone
-------------------------------------------------------------------------- 
Flux Tower Sites
 Southern Study Area:
SSA-FEN-SE501  F0L9T  104.61798W   53.80206N    525159.8    5961566.6  13
SSA-OBS-SE501  G8I4T  105.11779W   53.98717N    492276.5    5982100.5  13
SSA-OJP-SE501  G2L3T  104.69203W   53.91634N    520227.7    5974257.5  13
SSA-YJP-SE501  F8L6T  104.64529W   53.87581N    523320.2    5969762.5  13
SSA-9OA-SE501  C3B7T  106.19779W   53.62889N    420790.5    5942899.9  13
SSA-9YA-SE501  D0H4T  105.32314W   53.65601N    478644.1    5945298.9  13
-------------------------------------------------------------------------- 
 Northern Study Area:
NSA-OBS-SE501  T3R8T   98.48139W   55.88007N    532444.5    6192853.4  14
NSA-OJP-SE501  T7Q8T   98.62396W   55.92842N    523496.2    6198176.3  14
NSA-YJP-SE501  T8S9T   98.28706W   55.89575N    544583.9    6194706.9  14
NSA-BVP-SE501  T4U6T   98.02747W   55.84225N    560900.6    6188950.7  14
NSA-FEN-SE501  T7S1T   98.42072W   55.91481N    536207.9    6196749.6  14
-------------------------------------------------------------------------- 
Auxiliary Sites
 Southern Study Area:
SSA-9BS-SE501  D0H6S  105.29534W   53.64877N    480508.7    5944263.4   13
SSA-9BS-SE501  G2I4S  105.13964W   53.93021N    490831.4    5975766.3   13
SSA-9BS-SE501  G2L7S  104.63785W   53.90349N    523793.6    5972844.3   13
SSA-9BS-SE501  G6K8S  104.75900W   53.94446N    515847.9    5977146.9   13
SSA-9BS-SE501  G9I4S  105.11805W   53.99877N    492291.2    5983169.1   13
SSA-9JP-SE501  F5I6P  105.11175W   53.86608N    492651.3    5968627.1   13
SSA-9JP-SE501  F7J0P  105.05115W   53.88336N    496667.0    5970323.3   13
SSA-9JP-SE501  F7J1P  105.03226W   53.88211N    497879.4    5970405.6   13
SSA-9JP-SE501  G1K9P  104.74812W   53.90880N    516546.7    5973404.5   13
SSA-9JP-SE501  G4K8P  104.76401W   53.91883N    515499.1    5974516.6   13
SSA-9JP-SE501  G7K8P  104.77148W   53.95882N    514994.2    5978963.8   13
SSA-9JP-SE501  G8L6P  104.63755W   53.96558N    523778.0    5979752.7   13
SSA-9JP-SE501  G9L0P  104.73779W   53.97576N    517197.7    5980856.0   13
SSA-9JP-SE501  I2I8P  105.05107W   54.11181N    496661.4    5995963.1   13
SSA-ASP-SE501  B9B7A  106.18693W   53.59098N    421469.8    5938447.2   13
SSA-ASP-SE501  D6H4A  105.31546W   53.70828N    479177.5    5951112.1   13
SSA-ASP-SE501  D6L9A  104.63880W   53.66879N    523864.0    5946733.2   13
SSA-ASP-SE501  D9G4A  105.46929W   53.74019N    469047.1    5954718.4   13
SSA-MIX-SE501  D9I1M  105.20643W   53.72540N    486379.7    5952989.7   13
SSA-MIX-SE501  F1N0M  104.53300W   53.80594N    530753.7    5962031.8   13
SSA-MIX-SE501  G4I3M  105.14246W   53.93750N    490677.3    5976354.9   13
SSA-CLR-SE501  FRSHCL 104.69194W   53.91639N    520205.2    5974269.4   13
-------------------------------------------------------------------------- 
 Northern Study Area:
NSA-9BS-SE501  S8W0S   97.84024W   55.76824N    572761.9    6180894.9   14
NSA-9BS-SE501  T0P7S   98.82345W   55.88371N    511043.9    6193151.1   14
NSA-9BS-SE501  T0P8S   98.80225W   55.88351N    512370.1    6193132.0   14
NSA-9BS-SE501  T0W1S   97.80937W   55.78239N    574671.7    6182502.0   14
NSA-9BS-SE501  T3U9S   97.98339W   55.83083N    563679.1    6187719.2   14
NSA-9BS-SE501  T4U8S   97.99325W   55.83913N    563048.2    6188633.4   14
NSA-9BS-SE501  T4U9S   97.98364W   55.83455N    563657.5    6188132.8   14
NSA-9BS-SE501  T5Q7S   98.64022W   55.91610N    522487.2    6196800.5   14
NSA-9BS-SE501  T6R5S   98.51865W   55.90802N    530092.0    6195947.0   14
NSA-9BS-SE501  T6T6S   98.18658W   55.87968N    550887.9    6192987.9   14
NSA-9BS-SE501  T7R9S   98.44877W   55.91506N    534454.5    6196763.6   14
NSA-9BS-SE501  T7T3S   98.22621W   55.89358N    548391.8    6194505.6   14
NSA-9BS-SE501  T8S4S   98.37111W   55.91689N    539306.4    6197008.6   14
NSA-9BS-SE501  U5W5S   97.70986W   55.90610N    580655.5    6196380.8   14
NSA-9BS-SE501  U6W5S   97.70281W   55.91021N    581087.8    6196846.5   14
NSA-9JP-SE501  99O9P   99.03952W   55.88173N    497527.8    6192917.5   14
NSA-9JP-SE501  Q3V3P   98.02473W   55.55712N    561517.9    6157222.2   14
NSA-9JP-SE501  T7S9P   98.30037W   55.89486N    543752.4    6194599.1   14
NSA-9JP-SE501  T8Q9P   98.61050W   55.93219N    524334.5    6198601.4   14
NSA-9JP-SE501  T8S9P   98.28385W   55.90456N    544774.3    6195688.9   14
NSA-9JP-SE501  T8T1P   98.26269W   55.90539N    546096.3    6195795.3   14
NSA-9JP-SE501  T9Q8P   98.59568W   55.93737N    525257.1    6199183.2   14
NSA-9OA-SE501  T2Q6A   98.67479W   55.88691N    520342.0    6193540.7   14
NSA-ASP-SE501  P7V1A   98.07478W   55.50253N    558442.1    6151103.7   14
NSA-ASP-SE501  Q3V2A   98.02635W   55.56227N    561407.9    6157793.5   14
NSA-ASP-SE501  R8V8A   97.89260W   55.67779N    569638.4    6170774.8   14
NSA-ASP-SE501  S9P3A   98.87621W   55.88576N    507743.3    6193371.6   14
NSA-ASP-SE501  T4U5A   98.04329W   55.84757N    559901.6    6189528.2   14
NSA-ASP-SE501  T8S4A   98.37041W   55.91856N    539348.3    6197194.6   14
NSA-ASP-SE501  V5X7A   97.48565W   55.97396N    594506.1    6204216.6   14
NSA-ASP-SE501  W0Y5A   97.33550W   56.00339N    603796.6    6207706.6   14
NSA-MIX-SE501  Q1V2M   98.03769W   55.54568N    560718.3    6155937.3   14
NSA-MIX-SE501  T0P5M   98.85662W   55.88911N    508967.7    6193747.3   14
NSA-BRS-SE501  BRSOL   98.28889W   55.90528N    544441.4    6195777.7   14
NSA-TMK-SE501  TAMRK   98.42111W   55.91583N    536165.1    6196874.8   14
NSA-BRN-SE501  BRNJP   99.04383W   55.88184N    497240.1    6192940.9   14
-------------------------------------------------------------------------- 

7.1.2 Spatial Coverage Map

Not available.

7.1.3 Spatial Resolution

The 15-degree FOV of the SE-590 yielded a ground resolution of 79 m from the 300 
m altitude.

7.1.4 Projection

Not applicable.

7.1.5 Grid Description

Not applicable.

7.2 Temporal Characteristics

7.2.1 Temporal Coverage

Observations were made during all three BOREAS 1994 IFCs, which occurred during 
the following periods:

IFC-1   24-May    - 16-June
IFC-2   19-July   - 10-August
IFC-3   30-August - 19-September

Measurements were made as conditions permitted during each IFC.

7.2.2 Temporal Coverage Map

Observations were made at several sites on the following dates:

-----------------------------
Date	Study Area
-----------------------------
 31-May-94 	SSA
  1-Jun-94	SSA
  4-Jun-94	SSA
  6-Jun-94	SSA
  7-Jun-94	SSA
  8-Jun-94	NSA
 10-Jun-94	NSA
 21-Jul-94	NSA
 22-Jul-94	SSA
 23-Jul-94	SSA
 24-Jul-94	SSA
 25-Jul-94	SSA
 28-Jul-94	SSA
  4-Aug-94	NSA
  8-Aug-94	NSA
  6-Sep-94	NSA
  8-Sep-94	NSA
  9-Sep-94	NSA
 13-Sep-94	NSA
 15-Sep-94	SSA
 16-Sep-94	SSA

7.2.3 Temporal Resolution

Measurements were collected as conditions permitted during each IFC.  In 
general, the helicopter would hover 1-2 minutes for each observation (consisting 
of an average number of 20-25 scans).  Each site was visited as often as 
possible during each IFC, with priority given to tower flux sites and category 1 
auxiliary sites.  Helicopter flight time was limited to approximately 2 hours by 
fuel constraints.  As many sites as possible were visited during each flight.

7.3 Data Characteristics

Data characteristics are defined in the companion data definition file 
(rs3se590.def).

7.4 Sample Data Record

Sample data format shown in the companion data definition file (rs3se590.def).

8. Data Organization

8.1 Data Granularity

All of the Reflectance Measured from a Helicopter-Mounted SE-590 data are 
contained in one dataset.

8.2 Data Format(s)

The data files contain a series of numerical and character fields of varying 
length separated by commas.  The character fields are enclosed within single 
apostrophe marks.  There are no spaces between the fields.  Sample data records 
are shown in the companion data definition file (rs3se590.def).

9. Data Manipulations

9.1 Formulae

9.1.1 Derivation Techniques and Algorithms

From Vermote et al. (1997):

"Two atmospheric processes modify the solar radiance reflected by a target when 
viewed from space:  absorption by the gases (when observation bands are 
overlapping gaseous absorption bands) and scattering by the aerosols and the 
molecules.  If the gaseous absorption can be de-coupled from scattering as if 
the absorbents were located above the scattering layers, as assumed in the 6S 
code, the equation of transfer for a Lambertian homogeneous target of 
reflectance P_SFC at sea level altitude viewed by a satellite sensor (under 
zenith angle of view theta_v and azimuth angle of view phi_v) and illuminated by 
sun (theta_s, phi_s) is...:

P_TOA(theta_s, theta_v, phi_s-phi_v) =

T_g(theta_s, theta_v) * 

[P_R+A + T_dn(theta_s) * T_up(theta_v) * {P_SFC / (1 - S*P_SFC)}].    (1)

The various quantities are expressed in terms of equivalent reflectance P 
defined as P = pi * L /mu_s* E_s where L is the measured radiance, E_s is the 
solar flux at the top of the atmosphere, and mu_s = cos(theta_s) where theta_s 
is the solar zenith angle."

In addition, note the following notation (Vermote et al, 1997):

     T_g       Gaseous transmission of water vapor, carbon dioxide, oxygen
               and ozone.
     P_TOA     Reflectance at the top of the atmosphere.
     P_R+A     Intrinsic reflectance of the molecule + aerosol layer.
     T_dn      Total transmission of the atmosphere on the path between the
               sun and the surface.
     T_up      Total transmission of the atmosphere on the path between the
               surface and the sensor.
     S         Spherical albedo of the atmosphere.

9.2 Data Processing Sequence

9.2.1 Processing Steps

The SE-590 sensor voltages were processed to at-sensor radiances (W/m2 sr mm) 
following procedures described in Markham et al. (1988). Calibration 
coefficients were obtained before and after the deployment at NASA GSFC and 
onsite during the deployment using a portable calibration apparatus. The 
individual data scans were examined and those with obvious spurious values (i.e. 
outliers in the distribution) were removed.

The mean helicopter SE-590 radiances and sunphotometer data collected by the 
onboard sunphotometer were then input into Version 4.0 of the 6S software 
(Vermote et al., 1997) to obtain at-surface reflectance factors corrected for 
atmospheric effects.  A surface-based network of sunphotometers supplemented the 
helicopter-based measurements of atmospheric conditions when the latter were
not available.

9.2.2 Processing Changes

None.

9.3 Calculations

9.3.1 Special Corrections/Adjustments

None.

9.3.2 Calculated Variables

See Section 9.1.1.

9.4 Graphs and Plots

Not included here.  See Loechel et al., 1996.

10. Errors

10.1 Sources of Error

Potential sources of error include radiometric calibration; spectral 
calibration; physical (environmental and human) conditions (including helicopter 
vibration, minor changes in helicopter altitude and inclination); atmospheric 
conditions, including atmospheric parameters estimated from the surface 
sunphotometer network; and the atmospheric correction algorithm (Vermote et al., 
1997).  Confidence intervals for the visible/near-infrared at-sensor radiance 
values presented in this data set are within 3%.  The possibility of errors 
being introduced into the data set increases with additional manipulations of 
the data.  For an in-depth discussion of error considerations, see Markham et 
al. (1988).

10.2 Quality Assessment

Visual quality assessment was performed during data collection.  See reference 
list and helicopter logs.

10.2.1 Data Validation by Source

None given.

10.2.2 Confidence Level/Accuracy Judgment

A thorough quantitative error analysis of this kind of data set is given in 
Markham et al. (1988). 

10.2.3 Measurement Error for Parameters

Confidence intervals for the at-sensor radiance values presented in this data 
set are within 3%.

10.2.4 Additional Quality Assessments

See helicopter logs.  Also, see reference:  Walthall et al., 1997.

10.2.5 Data Verification by Data Center

A visual examination of all of the helicopter-mounted SE-590 at-surface 
reflectances reveal artifacts from the atmosphere in all of the spectra.  This 
is especially obvious in the oxygen and water absorption regions in the near- 
infrared.  That all the atmospheric effects have not been removed from the near-
infrared bands causes one to suspect the atmospheric corrections in the visible 
bands as well.  

While the atmospheric effects on at-surface reflectance at any given wavelength 
may be small, these effects may cause significant problems in some types of 
hyperspectral analyses.  Some analysis techniques look at band-to-band 
covariances or derivatives.  The atmospheric effects are nonlinear with 
wavelength, and thus, by not completely removing these effects, the data become 
questionable for those types of analyses.

11. Notes

11.1 Limitations of the Data

See section 10.2.5.

11.2 Known Problems with the Data

Caution should be used when using a band reflectance in the near-infrared 
calculated with a gaseous transmittance much under 0.9; i.e., use caution in the 
oxygen band (~760 nm) and the water vapor absorption band (~820 nm) -- where 
absorption effects can be under/overestimated, respectively.  It is suggested 
that a neighboring band not affected by gaseous absorption be used, which seems 
to characterize surface absorption effects well through the near-infrared.

Data collected over sparse canopies and with extreme solar geometry (i.e., early 
morning/late afternoon observations) will contain substantial amounts of shadow, 
which may complicate the retrieval of surface vegetation parameters.

In addition, isolated atmospheric events (such as forest fires or scattered 
cloudiness) reduce the certainty in the atmospheric correction.  The use of 
surface-measured atmospheric variables contributes to error in the data set in 
those cases.

11.3 Usage Guidance

See Sections 10.2.5, 11.1, and 11.2.

11.4 Other Relevant Information

None given.

12. Application of the Data Set

Research questions that may be examined with this data include:

  Retrieval of leaf area index (LAI) from spectral vegetation index.
  Scaling of spectral response in boreal regions (in combination with other
   BOREAS data sets).

13. Future Modifications and Plans

None.

14. Software

14.1 Software Description

The software used in the atmospheric correction of this data set was 6S, Version 
3.2 (Vermote et al., 1997).

14.2 Software Access

This software is public domain and available via anonymous ftp at 
kratmos.gsfc.nasa.gov.

15. Data Access

15.1 Contact Information

Ms. Beth Nelson
BOREAS Data Manager
NASA GSFC
Greenbelt, MD 
(301) 286-4005
(301) 286-0239 (fax)
Elizabeth.Nelson@gsfc.nasa.gov

15.2 Data Center Identification

See Section 15.1.

15.3 Procedures for Obtaining Data

Users may place requests by telephone, electronic mail, or fax.

15.4 Data Center Status/Plans

The RSS-03 helicopter SE-590 data are available from the Earth Observing System 
Data and Information System (EOSDIS), Oak Ridge National Laboratory (ORNL) 
Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: 

ORNL DAAC User Services
Oak Ridge National Laboratory
Oak Ridge, TN 
(423) 241-3952
ornldaac@ornl.gov
ornl@eos.nasa.gov

16. Output Products and Availability

16.1 Tape Products

None.

16.2 Film Products

None.

16.3 Other Products

The data are available as American Standard Code for Information Interchange 
(ASCII) files of helicopter SE-590 data.

17. References

17.1 Platform/Sensor/Instrument/Data Processing Documentation

Markham, B.L., D.L. Williams, J.R. Schafer, F. Wood, and M.S. Kim. 1995. 
Radiometric characterization of diode-array field spectroradiometers.  Remote 
Sensing of Environment, vol. 51, pp. 317-330.

17.2 Journal Articles and Study Reports

Loechel, S., C.L. Walthall, E. Brown de Colstoun, J. Chen, and B. Markham.  
1996.  Spatial and temporal variability of surface cover at BOREAS using 
reflectance from a helicopter platform. International Geosciences and Remote 
Sensing Symposium (IGARSS), Lincoln, NE.

Markham, B.L., F.M. Wood Jr., and S.P. Ahmad. 1988.  Radiometric calibration of 
thereflective bands of NS001-thematic mapper simulator (TMS) and modular 
multispectral radiometers (MMR).  In Recent Advances in Sensors Radiometry and 
Data Processing for Remote Sensing Proc. SPIE 24, pp. 96-108.

Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment 
Plan. Version 1994-3.0 NASA BOREAS Report (EXPLAN 94).

Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment 
Plan. Version 1996-2.0 NASA BOREAS Report (EXPLAN 96).

Sellers, P. and F. Hall. 1997. BOREAS Overview Paper. JGR BOREAS Special Issue, 
201.

Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere 
Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94).

Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere 
Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96).

Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. 
Cihlar, M.G. Ryan, B. Goodison, P. Cril,l K.J. Ranson, D. Lettenmaier, and D.E. 
Wickland. 1995.  The boreal ecosystem-atmosphere study (BOREAS): an overview and 
early results from the 1994 field year. Bulletin of the American Meteorological 
Society. 76(9):1549-1577.

Strebel, D.E., D.R. Landis, K.F. Huemmrich, and W.W. Meeson.  1994.  Collected 
Data of The First ISLSCP Field Experiment, Volume 1:  Surface Observations and 
Non-Image Data Sets.  Published on CD-ROM by NASA.

Vermote, E., D. Tanre, and J. Morcrette. 1997.  Second simulation of the 
satellitesignal in the solar spectrum, 6S: an overview. IEEE Trans. Geosci. 
Remote Sens., vol. 35, no. 3, pp. 675.

Vermote, E., D. Tanre, J.L. Deuze, M. Herman, and J.J. Morcrette.  1996.  Second 
simulation of the satellite signal in the solar spectrum (6S), 6S User Guide 
Version 1, October 7, 1996. University of Maryland/Laboratoire d'Optique 
Atmospherique,  216 pp. (available via anonymous ftp at kratmos.gsfc.nasa.gov).

Walter-Shea, Elizabeth A. and Larry L. Biehl, 1990 "Measuring Vegetation 
Spectral Properties", Remote Sensing Reviews Chapter 11, Edited by Narendra Goel 
and John Norman, Vol. 5, pp 179-205.

Walthall, C., and E. Middleton. 1992. Assessing spatial and seasonal variations 
in grasslands with spectral reflectances from a helicopter platform.  J. 
Geophys. Res., vol. 97, no. D17, pp. 18905-18912.

Walthall, C., D.L. Williams, B. Markham, J. Kalshoven, and R. Nelson. 1996.  
Development and present configuration of the NASA GSFC/WFF helicopter-based 
remote sensing system.  International Geosciences and Remote Sensing Symposium 
(IGARSS). Lincoln, NE.

17.3 Archive/DBMS Usage Documentation

None.

18. Glossary of Terms

None.

19. List of Acronyms

    6S      - Second Simulation of the Satellite Signal in the Solar Spectrum
    AGL     - Above Ground Level
    ASCII   - American Standard Code for Information Interchange
    BOREAS  - BOReal Ecosystem-Atmosphere Study
    BORIS   - BOREAS Information System
    BSQ     - Band Sequential
    CCD     - Charge-Coupled Device (??)
    DAAC    - Distributed Active Archive Center
    DN      - Digital Number
    EOS     - Earth Observing System
    EOSDIS  - EOS Data and Information System
    FOV     - Field of View
    GSFC    - Goddard Space Flight Center
    IFC     - Intensive Field Campaign
    IFOV    - Instantaneous Field of View
    LAI     - Leaf Area Index
    MMR     - Modular Multiband Radiometer
    NASA    - National Aeronautics and Space Administration
    NSA     - Northern Study Area
    ORNL    - Oak Ridge National Laboratory
    PANP    - Prince Albert National Park
    RSS     - Remote Sensing Science
    SE-590  - Spectron Engineering spectroradiometer 
    SSA     - Southern Study Area
    SWIR    - Short-Wave Infrared
    TM      - Thematic Mapper
    URL     - Uniform Resource Locator
    UTM     - Universal Transverse Mercator
    VIS/NIR - Visible/Near-Infrared
    WFF     - Wallops Flight Facility

20. Document Information

20.1 Document Revision Date

Written:            31-Oct-1995
Last Updated:       02-Jul-1998

20.2 Document Review Date(s)

BORIS Review:       30-Nov-1997
Science Review:     

20.3 Document ID

20.4 Citation

If this data set is referenced by another investigator, please acknowledge the 
RSS03 investigation team and this document.

20.5 Document Curator

20.6 Document URL


KEYWORDS:

reflectance
radiometer
atmospheric correction
helicopter

RSS03_Helo_SE590.doc
07/07/98