Engineering topics

Markham, B. L.

Publications and source records attributed to Markham, B. L..

At least 19 records

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 NTRS1992

Surface reflectance retrieval from satellite and aircraft sensors - Results of sensors and algorithm comparisons during FIFE

Visible to shortwave infrared radiometric data collected by a number of remote sensing instruments on aircraft and satellite platforms were compared over common areas in the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) site on August 4, 1989, to assess their radiometric consistency and the adequacy of atmospheric correction algorithms. The instruments in the study included the Landsat 5 Thematic Mapper (TM), the SPOT 1 high-resolution visible (HRV) 1 sensor, the NS001 Thematic Mapper simulator, and the modular multispectral radiometers (MMRs). Atmospheric correction routines analyzed were an algorithm developed for FIFE, LOWTRAN 7, and 5S. A comparison between corresponding bands of the SPOT 1 HRV 1 and the Landsat 5 TM sensors indicated that the two instruments were radiometrically consistent to within about 5 percent. Retrieved surface reflectance factors using the FIFE algorithm over one site under clear atmospheric conditions indicated a capability to determine near-nadir surface reflectance factors to within about 0.01 at a reflectance of 0.06 in the visible (0.4-0.7 microns) and about 0.30 in the near infrared (0.7-1.2 microns) for all but the NS001 sensor. All three atmospheric correction procedures produced absolute reflectances to within 0.005 in the visible and near infrared. In the shortwave infrared (1.2-2.5 microns) region the three algorithms differed in the retrieved surface reflectances primarily owing to differences in predicted gaseous absorption. Although uncertainties in the measured surface reflectance in the shortwave infrared precluded definitive results, the 5S code appeared to predict gaseous transmission marginally more accurately than LOWTRAN 7.

Markham, B. L.↗

NASA NTRS1992

Algorithm for atmospheric corrections of aircraft and satellite imagery

A simple and fast atmospheric correction algorithm is described which is used to correct radiances of scattered sunlight measured by aircraft and/or satellite above a uniform surface. The atmospheric effect, the basic equations, a description of the computational procedure, and a sensitivity study are discussed. The program is designed to take the measured radiances, view and illumination directions, and the aerosol and gaseous absorption optical thickness to compute the radiance just above the surface, the irradiance on the surface, and surface reflectance. Alternatively, the program will compute the upward radiance at a specific altitude for a given surface reflectance, view and illumination directions, and aerosol and gaseous absorption optical thickness. The algorithm can be applied for any view and illumination directions and any wavelength in the range 0.48 micron to 2.2 microns. The relation between the measured radiance and surface reflectance, which is expressed as a function of atmospheric properties and measurement geometry, is computed using a radiative transfer routine. The results of the computations are presented in a table which forms the basis of the correction algorithm. The algorithm can be used for atmospheric corrections in the presence of a rural aerosol. The sensitivity of the derived surface reflectance to uncertainties in the model and input data is discussed.

Fraser, R. S.↗

NASA NTRS1992

Atmospheric correction and calibration during KUREX-91

The results of the aerosol optical thickness and water column abundance measurements performed with an eight-channel sun photometer during the KUREX-91 experiment are presented. Calibration of the sun photometer was performed at mountain sites before and after the field experiment. Subsequent to the field experiment, the sun photometer's response was compared with other instruments at many locations. Calibration results and the measurements are discussed.

Halthore, R. N.↗

NASA NTRS1989

Spatial degradation of satellite data

Consideration is given to a technique for spatially degrading high-resolution satellite data to produce comparable data sets over a range of coarser resolutions. Landsat MSS data is used to produce seven spatial resolution data sets by applying a spatial filter designed to simulate sensor response. Also, spatial degradation of coarse resolution data to provide data compression for the production of global-scale data sets is examined. NOAA AVHRR Global Area Coverage data is compared to other sampling procedures. It is found that sampling procedures that incorporate averaging result in decreased variance, while sampling procedures adopting single-value selection have higher variances and produce data values comparable with those from the original data.

Justice, C. O.↗

NASA NTRS1988

Spatial Resolution Requirements for MODIS-N

An empirical investigation of the required spatial resolution for MODIS-N is outlined. It is based on 5 LANDSAT multispectral scanner system images of the normalized difference vegetation index degraded to resolutions between 250 m and 4000 m. Pairs of images from different dates were registered and difference images were generated. Fourier analysis indicates that resolutions finer than 1 km are highly desirable for change detection. A sensor with a resolution of 500 m is recommended as providing the best compromise between detail of changes detected and the size of the resultant data volume, but other options are also suggested.

Townshend, J. R. G.↗

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 NTRS1986

Convection in the vertical midplane of a horizontal cylinder Comparison of two-dimensional approximations with three-dimensional results

Experimental results and numerical data on the flow characteristics of core-driven and boundary-layer-driven regimes (CDRs) and (BLDRs) are compared to two-dimensional solutions for heated convective flow in the vertical midplane of a horizontal cylinder. The data were obtained from laser Doppler velocimetry (LDA) measurements and from three-dimensional numerical solutions. It is shown that the approximate solutions gave the correct Rayleigh-number-dependences and distributions for the velocities in the CDR and BLDR regimes. However, the transition between the CDR and the BLDR, as well as the magnitude of the distribution of velocity components, were found to be dependent on the type of two-dimensional approximation selected. In the case of CDR, core velocities were overestimated by as much as 30 percent by the two-dimensional approximations; and in the case of BLDR, the core velocities were overestimated by 40-50 percent as compared to the measured velocities. A schematic illustration of the flow patterns in the cylinder is provided.

Bontoux, P.↗

NASA NTRS1985

The Landsat sensor's spatial responses

Based on the geometrical characteristics of the Landsat-4 and Landsat-5 Thematic Mapper (TM) and Multispectral Scanner (MSS), functions defining their spatial responses are derived, i.e., transfer functions (TF's) and line-spread functions (LSF's). These design LSF's and TF's are modified based on prelaunch component and system measurements to provide improved estimates. The two MSS instruments were comparable at their temperatures of best focus; separate calculations were performed for bands 1 and 3, band 2, and band 4. The presample nadir effective instantaneous fields of view, based on the 0.5 modulation transfer function (MTF) criteria, are 70-75 m in the track direction and 79-82 m in the scan direction. For the TM instruments, more extensive prelaunch measurements were available. LSF's derived from component measurements differed from the limited measured LSF data only in the ringing response/overshoot behavior.

Markham, B. L.↗

NASA NTRS1985

Landsat-4 and Landsat-5 MSS coherent noise - Characterization and removal

The Multispectral Scanner (MSS) remote sensing instrument carried by Landsat-4 and Landsat-5 is similar to MSS instruments carried by Landsat-1, Landsat-2, and Landsat-3. However, the addition of the Thematic Mapper (TM) instrument to Landsat-4 and Landsat-5 required several design changes in the MSS instruments carried on these satellites because of the lower orbit and new satellite platform. Data from the MSS onboard the Landsat-4 and Landsat-5 satellites were found to be generally comparable to the data obtained in the case of the earlier Landsat MSSs. However, a coherent noise pattern was observed in the Landsat-4 MSS data. In the present paper, the conduction of a noise analysis is discussed along with the noise characterization results, and a technique through which the Landsat-4 MSS coherent noise can be removed.

Tilton, J. C.↗

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

Impact of Thematic Mapper Sensor Characteristics on Classification Accuracy

A fixed effect, three factor (two levels per factor) analysis of variance was used to quantitatively assess the significance of the improved spectral, spatial and radiometric resolution capabilities of the LANDSAT-4 thematic mapper sensor relative to the familiar MSS sensor. TM data acquired over the Washington, D.C. area were progressively degraded in spectral, spatial and radiometric characteristics to simulate the MSS, and classification accuracies were derived in a consistent manner for all eight treatments in the ANOVA design. Statistical testing of the significance of differences in classification accuracies between treatments indicated that the increased number of spectral bands and the improved quantization capabilities afforded by the TM sensor design would lead to significant improvements in classification accuracies attainable relative to MSS. In contrast, however, the improved spatial resolution provided by the TM sensor did not enhance classification accuracy. This latter result was felt to be more a function of the type of classification algorithms available.

Williams, D. L.↗

NASA NTRS1985

Quick Look Analysis of TM Data of the Washington, District of Columbia, Area

Classification capabilities with TM data result from the interactive effects of all of the sensor's attributes which complicates a more quantitative evaluation of the effects of individual sensor improvements. An experiment conducted to quantify the effect of individual sensor parameters (e.g., spectral, spatial, and radiometric resolution) on classification accuracy is described on classification accuracy. Preliminary results obtained using TM data acquired over the Washington, D.C., area indicate that the additional number of spectral bands and quantization levels of the TM relative to the MSS increase capabilities for the recognition and discrimination of land cover/use categories by per-pixel maximum likelihood classification. The refinement of spatial resolution, however, seems to hinder classification.

Williams, D. L.↗

NASA NTRS1985

Preliminary Comparisons of the Information Content and Utility of TM Versus MSS Data

Some preliminary indications were provided as to the relative merits of actual TM data versus MSS data for land cover mapping related applications. Three analyses were designed which had sensitivity to the differences in spectral, spatial and radiometric parameters between the TM and MSS. In the water body analysis, a primarily spatially related test, the detectability of small uniform targets was examined. The principal components analysis, an examination of the inherent dimensionality of the data, was more spectrally and radiometrically related. The spectral clustering analysis, also heavily spectrally and radiometrically influenced, provided information on the types of targets separable on TM versus MSS data. These analyses were to be conducted with simultaneously collected LANDSAT-4 complete TM (7 band) and MSS (4 band) data. In actuality, 4-band TM data, and archived LANDSAT-2 MSS data of the same area were used.

Markham, B. L.↗

NASA NTRS1985

The effects of sensor advancements on Thematic Mapper data classification

Analyses of Landsat Thematic Mapper (TM) data were conducted to assess the effects of sensor advancements on the thematic classification of remote sensing data. The effects of altering three sensor characteristics (spatial resolution, data quantization, and spectral band configuration) from Landsat Multispectral Scanner (MSS) specifications were investigated using analysis-of-variance (ANOVA). Analyses were conducted on data from two TM scenes: Washington, D.C. (late autumn) and western Pennsylvania (late summer). Results indicate that the contribution of sensor advancements to thematic classification are highly dependent of spectral and spatial scene attributes.

Irons, J. R.↗

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.↗