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 Operat’l 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