BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted Barnes MMR Summary: The RSS-03 team acquired helicopter-based radiometric measurements of forested sites during BOREAS with a Barnes MMR. The data were collected in 1994 during the three BOREAS IFCs at numerous tower and auxiliary sites in both the NSA and SSA. The 15-degree FOV of the MMR yielded approximately 79 m from the 300 m altitude ground resolution. The MMR has seven spectral bands that are similar to the Landsat TM bands, ranging from the blue region to the thermal. The data are stored in tabular ASCII files. Note: An extensive helicopter log is available. 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 this helicopter log file. 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 the BOReal Ecosystem-Atmosphere Study (BOREAS) forested tower and auxiliary sites were taken from a helicopter platform with a nadir viewing angle. 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 Modular Multiband Radiometer (MMR) yielded an instantaneous field of view (IFOV) of approximately 79 m from the 300-m altitude typically flown. The MMR has seven spectral bands that are similar to the Landsat Thematic Mapper (TM) bands, ranging from the blue region to the thermal. 1.1 Data Set Identification BOREAS RSS-03 Reflectance Measured from a Helicopter-Mounted Barnes MMR 1.2 Data Set Introduction This documentation describes data acquired during the 1994 BOREAS Intensive Field Campaigns (IFCs) with a helicopter-mounted Barnes MMR. MMR radiances and ground sunphotometer data were used as input to Version 3.2 of the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) atmospheric correction software to obtain at-surface reflectance factors. The data are arranged in chronological order (date, time) and cover the period 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 was to acquire multispectral, bidirectional reflectance and surface temperature 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), spectroradiometer, and a video camera. A sun-tracking photometer was also deployed to provide data for calculations of irradiance and for atmospheric correction of the data. Estimates of atmospheric conditions were not available from the onboard sunphotometer at the time that this data set was processed; therefore, 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-surface and at-sensor reflectance, and at- sensor radiances acquired at tower and auxiliary sites during all three 1994 BOREAS IFCs. 1.5 Discussion These measurements were collected as part of the effort to evaluate models which 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 SE-590 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 Sunphotometer Measurements BOREAS RSS-12 Automated Ground Sunphotometer 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 USA (301) 504-6074 (301) 504-5031 (fax) cwalthal@asrr.arsusda.gov Contact 2 ---------------- Sara Loechel Faculty Research Assistant Department of Geography University of Maryland Remote Sensing and Modeling Laboratory/USDA Agricultural Research Service Beltsville, MD USA (301) 504-6823 (301) 504-5031 (fax) sloechel@asrr.arsusda.gov Contact 3 ------------- Jaime Nickeson Raytheon STX Corporation NASA GSFC Greenbelt, Maryland (301) 286-3373 (301) 286-0239 (fax) Jaime.Nickeson@ltpmail.gsfc.nasa.gov 3. Theory of Measurements Light 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. The helicopter missions were designed to provide a rapid means of intensively spectrally characterizing vegetative cover at the BOREAS sites and to provide an intermediate scale of sampling between spectral measurements made at the surface and those made from higher altitude aircraft and spacecraft multispectral imaging devices. The MMR instrumentation was chosen to provide compatibility with surface-based radiometers and TM spacecraft sensors. 4. Equipment 4.1 Sensor/Instrument Description The primary instruments for the BOREAS deployment were the SE-590 Spectron Engineering spectroradiometer (SE-590), a Barnes 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, were mounted on an operator-controlled pointable mount that allows control of the view zenith and view azimuth directions independent of the heading of the aircraft. The MMR was developed in the late 1970s in response to the need for a field instrument for remote sensing by the National Aeronautics Space Administration (NASA) remote sensing community. Calibration considerations were integral to the design of this device. The device consists of eight sensors (four silicon and four lead sulfide detectors) with associated changeable optics for each. The serial number of the instrument used was 117. The voltages from the MMR are digitized with the use of an 18-channel analog-to- digital (A/D) converter, the Travelogger. The Travelogger is a standalone A/D system that runs on AC power while in the helicopter and outputs digital data to the hard disk of a PC also controlling the SE-590 via an RS-232 cable. For additional information on the instruments, see also Walthall et al. (1996) and Robinson et al. (1981). 4.1.1 Collection Environment 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. An extensive helicopter log of all IFC’s is available. Environmental, technical, instrumental, and operational conditions are noted for each observation where applicable. 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 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 is 9,500 lbs. 4.1.3 Source/Platform Mission Objectives The helicopter missions were designed to provide a rapid means of intensively spectrally characterizing sites and to provide an intermediate scale of sampling between the surface measurements and the higher altitude aircraft and spacecraft multispectral imaging devices. The MMR instrumentation was chosen to provide compatibility with surface-based radiometers and TM spacecraft sensors. 4.1.4 Key Variables Surface reflectance. 4.1.5 Principles of Operation System 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. The voltages from the MMR are digitized with the use of an 18-channel A/D converter, a standalone A/D system that runs on AC power while in the helicopter and outputs digital data to a PC. 4.1.6 Sensor/Instrument Measurement Geometry The NASA Goddard Space Flight Center (GSFC)/WFF helicopter-based optical remote sensing system was deployed to acquire canopy multispectral data with a Barnes MMR while hovering approximately 300 m AGL (Walthall et al., 1996). The 15- degree FOV of the MMR yielded a ground resolution of approximately 79 m at the nominal altitude of 300 m. 4.1.7 Manufacturer of Sensor/Instrument MMR (this device is no longer in production) Barnes Engineering Company 30 Commerce Road Stamford, CT 07904 4.2 Calibration Calibration of the MMR was performed according to the procedures described in Markham et al., 1988. Radiometric calibration and spectral calibration procedures were done 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 also used to calibrate the airborne instruments on other aircraft and some of the surface- based radiometric instrumentation. The MMR relative spectral response curves of the filters were well characterized prior to the field deployment. 4.2.1 Specifications The Barnes MMR produces analog voltage responses to scene radiance in eight spectral bands and to the instrument chopper and detector temperatures. The 8 wavebands are described below. Wavebands 1-4 have silicon detectors, wavebands 5-7 have lead sulfide detectors and waveband 8 has a Lithium Tantalum trioxide detector. The MMR's dimensions are 26.4 cm by 20.5 cm by 22.2 cm, and it weighs 6.4 kg. ---------------------------- MMR Wavelength Range Channel (microns) ---------------------------- 1 0.45 - 0.52 2 0.52 - 0.60 3 0.63 - 0.69 4 0.76 - 0.90 5 1.15 - 1.30 6 1.55 - 1.75 7 2.08 - 2.35 8 10.40 - 12.50 ---------------------------- 4.2.1.1 Tolerance Markham et al. (1988) summarize the calibration and instrument degradation during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE): "The changes in calibration of the MMR instruments were related to the extent of their use. In the silicon channels of the MMR, instruments used throughout the 4 field campaigns showed degradations of 3-4% between pre- and post-season calibrations. Strong temperature sensitivity in the lead-sulfide (PbS) channels, about +/-25% over a 15 °C range, which was reduced to +/-4% or less with temperature correction, led to greater uncertainty in these channels calibration... ." Note that MMR bands 1-4 use silicon detectors and bands 5-7 use lead-sulfide (PbS) detectors. Similar results are expected with the BOREAS calibrations. 4.2.2 Frequency of Calibration Radiometric calibration and spectral calibration procedures were done 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 None. 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/GSFC and WF) 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. A 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 a Barnes MMR while hovering approximately 300 meters above ground level (Walthall et al. 1996). The 15-degree FOV of the MMR yielded an IFOV at this altitude of approximately 79 m. Observations were made over various tower and auxiliary sites during all three 1994 IFCs. 6. Observations 6.1 Data Notes An extensive helicopter log is available. Environmental, technical, instrumental, and operational conditions are noted for each observation where applicable. 6.2 Field Notes See Section 6.1. 7. Data Description 7.1 Spatial Characteristics The helicopter visited all of the NSA and SSA tower and category-1 auxiliary sites. 7.1.1 Spatial Coverage Each site listed below was observed by this instrument at least once during the 1994 campaign at BOREAS: -------------------------------------------------------------------------- Site Id Grid Id Longitude Latitude UTM UTM UTM Easting Northing Zone -------------------------------------------------------------------------- Flux Tower Sites Southern Study Area: SSA-FEN-MMR01 F0L9T 104.61798W 53.80206N 525159.8 5961566.6 13 SSA-OBS-MMR01 G8I4T 105.11779W 53.98717N 492276.5 5982100.5 13 SSA-OJP-MMR01 G2L3T 104.69203W 53.91634N 520227.7 5974257.5 13 SSA-YJP-MMR01 F8L6T 104.64529W 53.87581N 523320.2 5969762.5 13 SSA-9OA-MMR01 C3B7T 106.19779W 53.62889N 420790.5 5942899.9 13 SSA-9YA-MMR01 D0H4T 105.32314W 53.65601N 478644.1 5945298.9 13 -------------------------------------------------------------------------- Northern Study Area: NSA-OBS-MMR01 T3R8T 98.48139W 55.88007N 532444.5 6192853.4 14 NSA-OJP-MMR01 T7Q8T 98.62396W 55.92842N 523496.2 6198176.3 14 NSA-YJP-MMR01 T8S9T 98.28706W 55.89575N 544583.9 6194706.9 14 NSA-BVP-MMR01 T4U6T 98.02747W 55.84225N 560900.6 6188950.7 14 NSA-FEN-MMR01 T7S1T 98.42072W 55.91481N 536207.9 6196749.6 14 -------------------------------------------------------------------------- Auxiliary Sites Southern Study Area: SSA-9BS-MMR01 D0H6S 105.29534W 53.64877N 480508.7 5944263.4 13 SSA-9BS-MMR01 G2I4S 105.13964W 53.93021N 490831.4 5975766.3 13 SSA-9BS-MMR01 G2L7S 104.63785W 53.90349N 523793.6 5972844.3 13 SSA-9BS-MMR01 G6K8S 104.75900W 53.94446N 515847.9 5977146.9 13 SSA-9BS-MMR01 G9I4S 105.11805W 53.99877N 492291.2 5983169.1 13 SSA-9JP-MMR01 F5I6P 105.11175W 53.86608N 492651.3 5968627.1 13 SSA-9JP-MMR01 F7J0P 105.05115W 53.88336N 496667.0 5970323.3 13 SSA-9JP-MMR01 F7J1P 105.03226W 53.88211N 497879.4 5970405.6 13 SSA-9JP-MMR01 G1K9P 104.74812W 53.90880N 516546.7 5973404.5 13 SSA-9JP-MMR01 G4K8P 104.76401W 53.91883N 515499.1 5974516.6 13 SSA-9JP-MMR01 G7K8P 104.77148W 53.95882N 514994.2 5978963.8 13 SSA-9JP-MMR01 G8L6P 104.63755W 53.96558N 523778.0 5979752.7 13 SSA-9JP-MMR01 G9L0P 104.73779W 53.97576N 517197.7 5980856.0 13 SSA-9JP-MMR01 I2I8P 105.05107W 54.11181N 496661.4 5995963.1 13 SSA-ASP-MMR01 B9B7A 106.18693W 53.59098N 421469.8 5938447.2 13 SSA-ASP-MMR01 D6H4A 105.31546W 53.70828N 479177.5 5951112.1 13 SSA-ASP-MMR01 D6L9A 104.63880W 53.66879N 523864.0 5946733.2 13 SSA-ASP-MMR01 D9G4A 105.46929W 53.74019N 469047.1 5954718.4 13 SSA-MIX-MMR01 D9I1M 105.20643W 53.72540N 486379.7 5952989.7 13 SSA-MIX-MMR01 F1N0M 104.53300W 53.80594N 530753.7 5962031.8 13 SSA-MIX-MMR01 G4I3M 105.14246W 53.93750N 490677.3 5976354.9 13 -------------------------------------------------------------------------- Northern Study Area: NSA-9BS-MMR01 S8W0S 97.84024W 55.76824N 572761.9 6180894.9 14 NSA-9BS-MMR01 T0P7S 98.82345W 55.88371N 511043.9 6193151.1 14 NSA-9BS-MMR01 T0P8S 98.80225W 55.88351N 512370.1 6193132.0 14 NSA-9BS-MMR01 T0W1S 97.80937W 55.78239N 574671.7 6182502.0 14 NSA-9BS-MMR01 T3U9S 97.98339W 55.83083N 563679.1 6187719.2 14 NSA-9BS-MMR01 T4U8S 97.99325W 55.83913N 563048.2 6188633.4 14 NSA-9BS-MMR01 T4U9S 97.98364W 55.83455N 563657.5 6188132.8 14 NSA-9BS-MMR01 T5Q7S 98.64022W 55.91610N 522487.2 6196800.5 14 NSA-9BS-MMR01 T6R5S 98.51865W 55.90802N 530092.0 6195947.0 14 NSA-9BS-MMR01 T6T6S 98.18658W 55.87968N 550887.9 6192987.9 14 NSA-9BS-MMR01 T7R9S 98.44877W 55.91506N 534454.5 6196763.6 14 NSA-9BS-MMR01 T7T3S 98.22621W 55.89358N 548391.8 6194505.6 14 NSA-9BS-MMR01 T8S4S 98.37111W 55.91689N 539306.4 6197008.6 14 NSA-9BS-MMR01 U5W5S 97.70986W 55.90610N 580655.5 6196380.8 14 NSA-9BS-MMR01 U6W5S 97.70281W 55.91021N 581087.8 6196846.5 14 NSA-9JP-MMR01 99O9P 99.03952W 55.88173N 497527.8 6192917.5 14 NSA-9JP-MMR01 Q3V3P 98.02473W 55.55712N 561517.9 6157222.2 14 NSA-9JP-MMR01 T7S9P 98.30037W 55.89486N 543752.4 6194599.1 14 NSA-9JP-MMR01 T8Q9P 98.61050W 55.93219N 524334.5 6198601.4 14 NSA-9JP-MMR01 T8S9P 98.28385W 55.90456N 544774.3 6195688.9 14 NSA-9JP-MMR01 T8T1P 98.26269W 55.90539N 546096.3 6195795.3 14 NSA-9JP-MMR01 T9Q8P 98.59568W 55.93737N 525257.1 6199183.2 14 NSA-9OA-MMR01 T2Q6A 98.67479W 55.88691N 520342.0 6193540.7 14 NSA-ASP-MMR01 P7V1A 98.07478W 55.50253N 558442.1 6151103.7 14 NSA-ASP-MMR01 Q3V2A 98.02635W 55.56227N 561407.9 6157793.5 14 NSA-ASP-MMR01 R8V8A 97.89260W 55.67779N 569638.4 6170774.8 14 NSA-ASP-MMR01 S9P3A 98.87621W 55.88576N 507743.3 6193371.6 14 NSA-ASP-MMR01 T4U5A 98.04329W 55.84757N 559901.6 6189528.2 14 NSA-ASP-MMR01 T8S4A 98.37041W 55.91856N 539348.3 6197194.6 14 NSA-ASP-MMR01 V5X7A 97.48565W 55.97396N 594506.1 6204216.6 14 NSA-ASP-MMR01 W0Y5A 97.33550W 56.00339N 603796.6 6207706.6 14 NSA-MIX-MMR01 Q1V2M 98.03769W 55.54568N 560718.3 6155937.3 14 NSA-MIX-MMR01 T0P5M 98.85662W 55.88911N 508967.7 6193747.3 14 -------------------------------------------------------------------------- 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution At 300 m altitude, the 15-degree FOV of the MMR yielded a ground resolution of approximately 79 m. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Measurements were collected as conditions permitted during each IFC. Observations were made during all three BOREAS 1994 IFCs. IFC-1 24-May - 16-June IFC-2 19-July - 10-August IFC-3 30-August - 19-September 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 (rss3hmmr.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (rss3hmmr.def) 8. Data Organization 8.1 Data Granularity All of the Reflectance Measured from a Helicopter-Mounted Barnes MMR Data are contained in one dataset. 8.2 Data Format(s) The data files contain numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (rss3hmmr.def). 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms The approach used to calculate at surface reflectances comes 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 absorbants 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 seven spectral bands of the MMR used in this data set are: 0.45-0.52 µm (MMR1-blue), 0.51-0.52 µm (MMR2-green), 0.63-0.68 µm (MMR3-red) 0.75-0.88 µm (MMR4-near-infrared or infrared), 1.17-1.33 µm (MMR5-first middle infrared), 1.57-1.80 µm (MMR6-second middle infrared) and 2.08-2.37 µm (MMR7-farthest middle infrared). The MMR sensor voltages were processed to at-sensor radiances (W/m2 µm sr) 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 the obvious spurious values were removed. The mean helicopter MMR radiances, along with near-simultaneous sunphotometer data collected by the Remote Sensing Science (RSS)-11 automated ground network, were then input into Version 3.2 of 6S (Vermote et al., 1997) to obtain at-surface reflectance factors corrected for atmospheric effects. The 6S software is public domain and available via anonymous ftp at kratmos.gsfc.nasa.gov. The RSS-11 surface-based network of sunphotometers provided estimates of aerosol optical depths, which varied spatially and temporally, especially during the summer, due to the prevalence of smoke from forest fires. Sunphotometer measurements taken from the helicopter platform at data collection altitudes were not available at the time of this analysis. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None. 9.3.2 Calculated Variables At-sensor and at-surface reflectance factors. 9.4 Graphs and Plots None. 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). 10.2 Quality Assessment 10.2.1 Data Validation by Source Visual quality assessment was performed during data collection. See reference list and helicopter logs. 10.2.2 Confidence Level/Accuracy Judgment A thorough quantitative error analysis 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% of actual for the visible/near-infrared, 5% of actual for the mid- infrared, and +/- 5-6% for MMR channel 8. 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). 10.2.4 Additional Quality Assessments A complete quality assessment is provided in the helicopter logs. In addition see Walthall et al. (1997). 10.2.5 Data Verification by Data Center BOREAS Information System (BORIS) has performed some quality checks of the data in the process of loading the data into the data base. A subset of site information has been extracted and compared with TM reflectance values. 11. Notes 11.1 Limitations of the Data 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. 11.2 Known Problems with the Data A few spurious values are present in the data for MMR channel 8; The problems associated with these values have not yet been ascertained. In addition, helicopter data logs for IFCs 1, 2, and 3 are available. Input solar geometry (solar zenith angle and azimuth) used in Vermote et al (1997) atmospheric correction are in error by -1 hour for 08-June-1994 Flight A observations. 11.3 Usage Guidance None given. 11.4 Other Relevant Information See helicopter logs. 12. Application of the Data Set Research questions that may be examined with these 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 MMR 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 tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Markham, B.L., F.M. Wood Jr., and S.P. Ahmad. 1988. Radiometric calibration of the reflective 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. Robinson, B.F., R.E. Buckley, and J.A. Burgess. 1981. Performance evaluation and calibration of a modular multiband radiometer for remote sensing field research. SPIE Vol. 308, Contemporary Infrared Standards and Calibration, pp. 146-157. 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) Spring 1996, Lincoln, NE. Loechel, S.E., C.L Walthall, E. Brown de Colstoun, J. Chen, B.L. Markham and J. Miller. 1997. Variability of boreal forest reflectances as measured from a helicopter platform. Journal of Geophysical Research, Vol 102, No. D24, PP. 29, 495-29,503. Markham, B.L., F.M. Wood Jr., and S.P. Ahmad. 1988. Radiometric calibration of the reflective 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. Robinson, B. F., R. E. Buckley, and J.A. Burgess, 1981. Performance evaluation and calibration of a modular multiband radiometer for remote sensing field research, in Contemportary Infrared Standards and Calibration, Proc. SPIE Int. Soc. Opt. Eng., 308, 147-157.. 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. Crill, 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.J. Morcrette. 1997. Second simulation of the satellite signal 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). 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) Spring 1996, Lincoln NE. Walthall, C., S.E. Loechel, K.F. Huemmrich, E. Brown de Colstoun, J. Chen, B. L. Markham, J. Miller, and E.A. Walter-Shea. 1997. Spectral Information Content of the Boreal Forest, 10th International Colloquium on Physical Measurements and Signatures in Remote Sensing, International Society for Photogrammetry and Remote Sensing, Courchevel, France. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None given. 19. List of Acronyms 6S - Second Simulation of the Satellite Signal in the Solar Spectrum A/D - Analog-to-digital AGL - Above Ground Level ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CCD - Charge-Coupled Device DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FIFE - First ISLSCP Field Experiment FOV - Field of View GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign IFOV - Instantaneous Field of View ISLSCP - International Satellite Land Surface Climatology Project 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 (SE590) SSA - Southern Study Area TM - Thematic Mapper URL - Uniform Resource Locator UTM - Universal Transverse Mercator WFF - Wallops Flight Facility 20. Document Information 20.1 Document Revision Date Written: 31-Oct-1995 Last Updated: 05-Jun-1998 20.2 Document Review Date(s) BORIS Review: 30-Nov-1997 Science Review: 22-May-1998 20.3 Document ID 20.4 Citation If this data set is referenced by another investigator, please acknowledge this document and the paper by Loechel et al., 1997, listed in Section 17. 20.5 Document Curator 20.6 Document URL KEYWORDS: reflectance radiometer atmospheric correction helicopter RSS03_Helo_MMR.doc 06/11/98