https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1536&context=usgsstaffpub

Effects of Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper plus radiometric and geometric calibrations and corrections on landscape characterization

The Landsat-5 Thematic Mapper (TM) has been the workhorse of the Landsat system. Launched in 1984, it continues collecting data through the time frame of this paper. Thus, it provides an invaluable link to the past history of the land features of the Earth's surface, and it becomes imperative to provide an accurate radiometric calibration of the reflective bands to the user community. Previous calibration has been based on information obtained from prelaunch, the onboard calibrator, vicarious calibration attempts, and cross-calibration with Landsat-7. Currently, additional data sources are available to improve this calibration. Specifically, improvements in vicarious calibration methods and development of the use of pseudoinvariant sites for trending provide two additional independent calibration sources. The use of these additional estimates has resulted in a consistent calibration approach that ties together all of the available calibration data sources. Results from this analysis indicate a simple exponential, or a constant model may be used for all bands throughout the lifetime of Landsat-5 TM. Where previously time constants for the exponential models were approximately one year, the updated model has significantly longer time constants in bands 1-3. In contrast, bands 4, 5, and 7 are shown to be best modeled by a constant. The models proposed in this paper indicate calibration knowledge of 5% or better early in life, decreasing to nearly 2% later in life. These models have been implemented at the U.S. Geological survey earth resources observation and science (EROS) and are the default calibration used for all Landsat TM data now distributed through EROS.

Updated Radiometric Calibration for the Landsat-5 Thematic Mapper Reflective Bands

A coordinated effort on the part of several agencies has led to the specification of a definitive radiometric calibration record for the Landsat-5 thematic mapper (TM) for its lifetime since launch in 1984. The time-dependent calibration record for Landsat-5 TM has been placed on the same radiometric scale as the Landsat-7 enhanced thematic mapper plus (ETM+). It has been implemented in the National Landsat Archive Production Systems (NLAPS) in use in North America. This paper documents the results of this collaborative effort and the specifications for the related calibration processing algorithms. The specifications include (i) anchoring of the Landsat-5 TM calibration record to the Landsat-7 ETM+ absolute radiometric calibration, (ii) new time-dependent calibration processing equations and procedures applicable to raw Landsat-5 TM data, and (iii) algorithms for recalibration computations applicable to some of the existing processed datasets in the North American context. The cross-calibration between L...

A definitive calibration record for the Landsat-5 thematic mapper anchored to the Landsat-7 radiometric scale

For more than ten years, Landsat Thematic Mapper (TM) data has been collected of the Earth's surface. Although equipped with an internal calibrator, routine temporal analysis of the instrument's radiometry has not been performed. Recently, a project has been initiated to recover TM radiometric calibration data from the Landsat archive to form a TM calibration archive. This archive consists of calibration data collected at several different time scales: single orbit, instrument lifetime, and an intermediate scale. Analysis of these data is providing insights into how detector response, as well as internal calibrator performance, has changed over time. Initial results are shown that indicate changes in detector gain and characterization of instrument anomalies within a single orbit. Information obtained from this project will allow a more accurate calibration of data that is already in the Landsat archive. Additionally, it will directly impact development of correction algorithms for Landsat 7.

Radiometric calibration archive for Landsat TM

Studies have been completed into the spectral response of alkaline and other ultramafic rocks from arid and semi-arid regions. To date these rocks have not been investigated spectrally in a systematic fashion using the latest field and airborne imaging spectrometers. The objective was to determine how spectral geological techniques could be used to locate these rock types when they are exposed, weathered and reduced to residual soil. The data used in this study were spectra obtained from field spectrometers (PIMA and GER IRIS MkIV) and airborne scanners (GEOSCAN MkII, GER IS and HyMap). These data were gathered at four sites within Australia. The data processing software packages used for the analyses were commercially available image processing systems (is S'600and ENVI) and a modified version of PIMAVIEW for processing spectra. Spectra were measured, in the field and the laboratory, of alkaline and other ultramafic rocks to determine if they had diagnostic spectral absorption features. These studies demonstrated that there are diagnostic spectral absorption features common to alkaline and other ultramafic rocks including dunite, peridotite and serpentinite. The diagnostic spectrum in the SWIR2 region (2000nm to 2500nm) has absorption features located near 2300nm and 2380nm and results from Mg-OH bearing minerals including serpentine, talc and phlogopite. The VNIR spectra of these rocks also have distinct absorption features, but since these are caused by minerals that are common to a variety of rocks and soils, they have not been considered in this study. When weathered under arid and semi-arid conditions, ultramafic rocks break down into smectite clays, primarily saponite. Saponite has a similar spectral signature to the primary Mg-OH bearing minerals. Further weathering and removal of magnesium results in saponite altering to kaolinite and then to opaline silica. These minerals may occur in residual soils derived from ultramafic rocks. Spectral investigation of mixtures of saponite and other minerals showed that there are linear changes the absorption features of spectra, depth, wavelength and shape, as the proportion of saponite to other minerals varies. The ability to identify ultramafic rocks from the distribution of their diagnostic spectra was confirmed by analysing data obtained from surface samples and airborne scanners. The coincidence of results obtained from field studies and airborne scanner data signifies that data acquired remotely are as useful as spectra obtained in the field, for mapping the extent of ultramafic rocks. Present and past imaging systems have been investigated to determine the specifications required to suit this application. These investigations included sampling the spectra of ultramafic and background rocks with the band pass characteristics of various instruments. The signal-to-noise ratio that is required of scanner data to ensure it is useable was also studied. These studies indicated a specification for data of at least eight and preferably, thirty two channels in the SWIR2 (between 2000nm and 2500nm) obtained with a signalto- noise ratio in excess of 200: 1, ideally 400: 1 at 2200nm. Scanners producing data with these specifications can be used to locate ultramafic rocks from their spectral signature, whether exposed or covered by residual soils in a variety of geological environments. The success of applying these techniques will however depend on the spectral contrast between ultramafic rocks and their backgrounds. Rocks that produce Mg-OH bearing minerals or have near 2300nm absorption can result in areas being mistakenly identified as containing alkaline and other ultramafic rocks. However, in this study it was demonstrated that carbonate soils and rocks that have a near 2300nm absorption feature can be spectrally distinguished from alkaline ultramafic derived saponite using HyMap scanner data. In South Australia dolomite appears to have altered to saponite at surface but kimberlites in the area can still be detected by processing HyMap scanner data with spectral as opposed to conventional image processing techniques.

Surface detection of alkaline ultramafic rocks in semi-arid and arid terrains using spectral geological techniques

Preflight and in-orbit sensor and data measurements indicate that TM meets or exceeds most specifications. Measured spectral band edges meet instrument specifications in 12 out of 14 cases; there is ample dynamic range. The signal-to-noise ratio exceeds specifications, except for band 3, channel 4; and band 7 channel 7 is very noisy but still meets specifications. The modulation transfer function of channel 4, band 2, is smaller than specified. Registration errors between the primary focal plane (PFP) and the cold focal plane (CFP) are about 0.75 pixels along-scan and 0.2 pixels across scan. Forward and reverse scan discontinuities are well within ground-processing capabilities to rectify. Instrument gain variability, up to 7 percent for band 5, requires use of the internal calibration (IC) system to assure radiometric accuracy. Preliminary applications evaluation of image contents indicates that TM provides much better definition of edges than MSS.

Landsat-4 sensor performance

Preflight and in-orbit sensor and data measurements indicate that TM meets or exceeds most specifications. Measured spectral band edges meet instrument specifications in 12 out of 14 cases; there is ample dynamic range. The signal-to-noise ratio exceeds specifications, except for band 3, channel 4; and band 7 channel 7 is very noisy but still meets specifications. The modulation transfer function of channel 4, band 2, is smaller than specified. Registration errors between the primary focal plane (PFP) and the cold focal plane (CFP) are about 0.75 pixels along-scan and 0.2 pixels across scan. Forward and reverse scan discontinuities, are well within ground-processing capabilities to rectify. Instrument gain variability, up to 7% for band 5, requires use of the internal calibration (IC) system to assure radiometric accuracy. Preliminary applications evaluation of image contents indicates that TM provides much better definition of edges than MSS.

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J. L. Barker

Papers

Landsat-4 sensor performance

LANDSAT-4 sensor performance