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Barker, J. L.

Publications and source records attributed to Barker, J. L..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

LANDSAT 7: Early on-Orbit Results

As this article was being submitted in mid-March, 1999, Landsat 7 had been cleared for an official launch date of April, 15, 1999, approximately 4 - 5 weeks prior to the Portland ASPRS conference. Although it is hoped that the presentation in Portland will be the first public status report on the in-orbit performance of the Landsat 7 spacecraft and the ETM+ instrument, it is impossible to discuss "early on-orbit performance" prior to launch. Therefore, we have chosen to summarize the overarching salient features of the Landsat 7 program, and we will point to some web sites where additional information about the program can be found (e.g., http://geo.arc.nasa.gov/sge/landsat/landsat. html). At this time, the Landsat Project Science Office is pleased to report that the performance of the ETM+ instrument appears to be very good. In addition to excellent instrument performance, a robust data acquisition plan has been developed with the goal of acquiring a seasonally-refreshed archive of global land observations at the EROS Data Center annually. A ground processing system is being implemented at EROS that will be capable of capturing, processing and archiving 250 Landsat scenes per day, and delivering 100 scene products to users each day. The cost of a systematically-processed Level 1 product will be less than $600, and there will be no copyright protection on the data. The net result is that the use of remote sensing data in our daily lives is expected to grow dramatically. This growth is expected to benefit all facets of the land remote sensing community.

Williams, D. L.↗
NASA NTRS1999

Pre-Launch Noise Characterization of the Landsat-7 Enhanced Thematic Mapper Plus (ETM Plus)

A noise characterization of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument was performed as part of a near-real time performance assessment and health monitoring program. Perl'ormance data for the integrated Landsat-7 spacecraft and ETM+ were collected before, during, and after the spacecraft thermal vacuum testing program at the Lockheed Martin Missiles and Space (LMMS) facilities in Valley Forge, PA. The Landsat-7 spacecraft and ETM+ instrument were successfully launched on April 15, 1999. The spacecraft and ETM+ are now nearing the end of the on orbit engineering checkout phase, and Landsat-7 is expected to be declared operational on or about July 15, 1999. A preliminary post-launch noise characterization was performed and compared with the pre-launch characterization. In general the overall noise levels in the ETM+ are at or below the specification levels. Coherent noise is seen in most bands, but is only operationally significant when imaging in (he panchromatic band (band 8). This coherent noise has an amplitude as high as approximately 3 DN (peak-to-peak, high gain) at the Nyquist rate of 104 kHz, and causes the noise levels in panchromatic band images at times to exceed the total noise specification by up to approximately 10%. However, this 104 kHz noise is now much weaker than it was prior to the successful repair of the ETM+ power supplies that was completed in May 1998. Weak and stable coherent noise at approximately 5 kHz is seen in all bands in the prime focal plane (bands 1-4 and 8) with the prime (side A) electronics. Very strong coherent noise at approximately 20 kHz is seen in a few detectors of bands 1 and 8, but this noise is almost entirely in the turn-around region between scans when the ETM+ is not imaging the Earth. Strong coherent noise was seen in 2 detectors of band 5 during some of the pre-launch testing; however, this noise seems to be temperature dependent, and has not been seen in the current on orbit environment. Strong 91 kHz coherent noise was observed in the redundant (side B) panchromatic band data after the completion of spacecraft thermal vacuum testing. The cause of this coherent noise was identified as a failed capacitor that was replaced prior to launch, and this noise has not been seen on orbit.

Pedelty, J. A.↗
NASA NTRS1999

Landsat 7: An Early Look at On-Orbit Performance

As this article was being submitted in mid-March, 1999, Landsat 7 had been cleared for an official launch date of April 15, 1999, approximately 2 and 1/2 months prior to the 21st Canadian Symposium on Remote Sensing. Since it is impossible to discuss "early on-orbit performance" prior to the actual launch of the satellite, we have chosen to briefly summarize the major features of the Landsat 7 program. Additional information can be found at several web sites which will summarized at the end of this paper. At this time, the Landsat Project Science Office is pleased to report that the performance of the ETM+ instrument appears to be very good. In addition to excellent instrument performance, a robust data acquisition plan has been developed with the goal of acquiring and systematically refreshing a global archive of land observations at the EROS Data Center annually. A ground processing system is being implemented at EROS that will be capable of capturing, processing and archiving 250 Landsat scenes per day, and delivering 100 scene products to users daily. In addition, the cost of a systematically-processed Level 1 product will be less than $600, and there will be no copyright protection on the data. The net result is that the use of remote sensing data in our daily lives is expected to grow dramatically. This growth is expected to benefit all facets of the land remote sensing community.

Williams, D. L.↗
NASA NTRS1999

Landsat-7 EMT+ On-Orbit Radiometric Calibration

Landsat-7 was launched on April 15, 1999 and completed its on orbit initialization and verification period on June 28, 1999. The ETM+ payload is similar to the TM sensors on previous Landsat satellites and incorporates two new devices to improve its absolute radiometric calibration. The Full Aperture Solar Calibrator (FASC) is a deployable diffuser panel. This device has been deployed 9 times to date, with a normal deployment schedule of once per month. The initial analysis of the FASC data has given absolute calibration results within 5% of the prelaunch integrating sphere calibrations and a range of variation of 2% between dates. The Partial Aperture Solar Calibrator (PASC), is a set of auxiliary optics that allows the ETM+ to view the sun through a reduced aperture. Data have normally been acquired on a daily basis with the PASC. Initial results with the PASC were encouraging, despite some unexpected saturation in the shortest wavelength band. The response of the ETM+ short wavelength (silicon) bands to the PASC increased initially and has begun to decrease in some of these bands. The longer wavelength (InSb) bands have shown up to 30% oscillations that vary between detectors within the band. Studies are ongoing to better characterize the response to the PASC. The ETM+ also incorporates an internal calibrator (IC), a shutter that oscillates in front of the focal plane that directs light from the internal calibrator lamps to the focal plane. The responses to this device are also varying, though differently than the PASC results. Both the IC and PASC results are attributable to the calibration devices as opposed to the ETM+ itself.

Markham, Brian L.↗
NASA NTRS1987

Thematic Mapper bandpass solar exoatmospheric irradiances

Based on solar irradiance data published by Neckel and Labs (1984) and Iqbal (1983), the solar exoatmospheric irradiances for Thematic Mapper (TM) bands 1, 2, 3, and 4 have been calculated. Results vary by up to 1 percent from previous published values, which were based on the earlier data of Neckel and Labs. For TM bands 5 and 7, integrated solar exoatmospheric irradiances have also been recalculated using solar irradiance data published by Labs and Neckel (1968), Arvesen et al. (1969), and Iqbal (1983). These irradiances vary by up to 6 percent from previously published results, which were based on data published by Thekaekara (1972).

Markham, B. L.↗
NASA NTRS1985

Spectral characterization of the Landsat Thematic Mapper sensors

Relative spectral response data for the Landsat-4 and Landsat-4 backup multispectral scanner subsystems (MSS), the protoflight and flight models, are presented and compared to similar data for the Landsat 1, 2 and 3 scanners. Channel (six channels per band) outputs for soil and soybean targets were simulated and compared within each band and between scanners.The principal differences between the spectral responses of the Landsat-4 scanners and previous scanners are discussed. The simulated Landsat-4 scanner outputs were 3 to 10 percent lower in the red band and 3 to 11 percent higher in the first near-IR band than previous scanners for the soybeans targets. The Landsat-4 scanners were generally more uniform from channel to channel within bands than previous scanners. In the upper-band edge of the red band of the protoflight scanner, one channel was markedly different (12 nm) from the rest. For a soybeans target, this nonuniformity resulted in a within-band difference of 6.2 percent in simulated outputs between channels.

Markham, B. L.↗
NASA NTRS1985

Relative Radiometric Calibration of LANDSAT TM Reflective Bands

Results and recommendations pertaining to the characterization of the relative radiometric calibration of the protoflight thematic mapper (TM/PF) on the LANDSAT-4 satellite are presented. Some preliminary pre-launch and in-orbit results are also included from the flight model (TM/F) on LANDSAT-5. A common scientific methodology and terminology is outlined for characterizing the radiometry of both TM sensors. The magnitude of the most significant sources of radiometric variability are discussed and methods are recommended for achieving the exceptional potential inherent in the radiometric precision and accuracy of the sensors.

Barker, J. L.↗
NASA NTRS1985

Thermal Band Characterization of the LANDSAT-4 Thematic Mapper

The initial characterization of the Thematic Mapper (TM) thermal band is reported including gain stability, gain relation to internal calibration, corrections for channel-to-channel and scan direction differences, an approximate comparison to ground truth, and a calculation of noise equivalent temperature difference. Updated calibration information is also presented.

Lansing, J. C.↗
NASA NTRS1985

LANDSAT-4 Science Characterization Early Results. Volume 4: Applications

The excellent quality of TM data allows researchers to proceed directly with applications analyses, without spending a significant amount of time applying various corrections to the data. The early results derived of TM data are discussed for the following applications: agriculture, land cover/land use, soils, geology, hydrology, wetlands biomass, water quality, and snow.

Barker, J. L.↗
NASA NTRS1984

Multispectral Scanner (MSS) Instrument Description

The MSS sensor image processing and resolution capabilities as well as a general system description are presented in chart form. Emphasis is placed on absolute radiometric calibration, video and wedge level timing sequence, focal plane dimensions, sampling sequence, and a description of the mirror coordinate systems.

Barker, J. L.↗
NASA NTRS1984

TM Digital Image Products for Applications

LANDSAT-4 Thematic Mapper (TM) digital image products recorded onto computer compatible tapes (CCTs), which were available for internal research purposes prior to August, 1983, are reviewed. The SCROUNGE image processing system at Goddard Space Flight Centr generated in tape formats: (1) raw band-sequential data (CCT-BT), generally used for internal transportation of digital data from one ground processing system to another; (2) calibrated data (CCT-AT), useful for reseachers doing radiometric characterization; and (3) geometrically resampled data (CCT-PT), the final product. The formats represent different steps in the process of producing fully-corrected TM data. The CCT-BT images are re-sequenced from telemetry format to image format, but are uncorrected radiometrically and geometrically. The CCT-AT images had data from two faulty data channels replaced and all data radiometrically calibrated. The CCT-PT images were resampled by cubic convolution procedures to provide a geometrically corrected image using satellite ephemeris and altitude data and scan-mirror correction data. The final product, the CCT-PT, is the one to which all of the radiometric and geometric corrections were applied.

Barker, J. L.↗
NASA NTRS1984

Spectral Characterization of the LANDSAT Thematic Mapper Sensors

Data collected on the spectral characteristics of the LANDSAT-4 and LANDSAT-4 backup thematic mapper instruments, the protoflight (TM/PF) and flight (TM/F) models, respectively, are presented and analyzed. Tests were conducted on the instruments and their components to determine compliance with two sets of spectral specifications: band-by-band spectral coverage and channel-by-channel within-band spctral matching. Spectral coverage specifications were placed on: (1) band edges - points at 50% of peak response, (2) band edge slopes - steepness of rise and fall-off of response, (3) spectral flatness - evenness of response between edges, and (4) spurious system response - ratio of out-of-band response to in-band response. Compliance with the spectral coverage specifications was determined by analysis of spectral measurements on the individual components contributing to the overall spectral response: filters, detectors, and optical surfaces.

Markham, B. L.↗
NASA NTRS1984

Pre-launch Absolute Radiometric Calibration of LANDSAT-4 Protoflight Thematic Mapper

From both scientific and applications perspectives, the usefulness of TM digital imagery is significantly determined by its radiometric characteristics. This includes both the accuracy to which the dynamic range is known and its radiometric reproducibility or precision. Results from several pre-launch tests with a 122-cm Integrating Sphere (IS) used as part of the absolute radiometric calibration experiments for the protoflight TM sensor carried on the LANDSAT-4 satellite are summarized and analyzed. Topics covered include TM radiometric calibration and sensitivity; the TM internal calibrator; and the dynamic range after calibration.

Barker, J. L.↗
NASA NTRS1984

Relative Radiometric Calibration of LANDSAT TM Reflective Bands

The characterization of the relative radiometric calibration of the protoflight Thematic Mapper sensor (TM/PF) is considered with focus on the variability and uncertainty of TM relative radiometry, including total variability as well as its systematic and random components. Emphasis is placed on identifying the magnitude and types of systematic errors, since these have the potential for being reduced during ground processing. Estimates of innate random variability, such as the standard deviation of a signal or its signal to noise ratio, are also important. The processing effects of radiometry are explored. Recommendations are given for engineering characterization, flight segment operations and ground processing.

Barker, J. L.↗
NASA NTRS1984

Thermal Band Characterization of LANDSAT-4 Thematic Mapper

A quick look monitor in the spacecraft control center was used to measure the TM Band 6 shutter background and the 34.7 C internal blackbody signal on over 50 dates. Comparison of relative internal gains between the four channels to prelaunch values showed changes over 9 months of up to 5%, while 512 x 512 subsections of the original 10 daytime scenes showed scene counts that ranged from 135 down to 62. A night scene of the Buffalo area was used to determine channel gain relative to the mean and to discern a systematic along scan pattern in a difference between forward and reverse scan counts of up to 0.5. A corrected digital image was produced and individual gains and offsets were calculated for the four channels. At satellite radiance was determine and noise equivalent temperature difference was calculated. The calibration data and the Buffalo scene, with the corrections and estimates of the atmospheric transmission and radiance, were used to make a temperature estimate for an area of Lake Erie of 21 C to 27 C. Local records of the temperature showed 21 C.

Lansing, J. C.↗