Geology topics

Gyanesh Chander

Publications and source records attributed to Gyanesh Chander.

27 records · Page 2Linked to original sources

USGS2008

Monitoring on-orbit stability of Terra MODIS and Landsat 7 ETM+ reflective solar bands using Railroad Valley Playa, Nevada (RVPN) test site

The Moderate Resolution Imaging Spectroradiometer (MODIS) Proto-Flight Model (PFM), launched on December 18, 1999, aboard NASA's Earth Observing System (EOS) Terra satellite has 20 reflective solar bands (RSB) with wavelengths ranging from 0.41 to 2.1 mum over a wide field of view (plusmn55deg). The Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensor was launched on April 15, 1999, and has six spectral bands located in the visible and shortwave infrared (SWIR) part of the electromagnetic spectrum (0.4 - 2.5 mum). The ETM+ belongs to the family of Thematic Mapper sensors flown on previous Landsat missions. In this study, over 75 cloud-free nadir near-simultaneous images over Railroad Valley Playa, Nevada (RVPN) were chosen covering entire missions of both sensors. RVPN (38.5degN and 115.7degW), located between the cities of Ely and Tonopah, Nevada, USA, is a high reflectance site with very high spatial, spectral, and temporal uniformity. It is referenced to the Worldwide Reference System-2 (WRS-2) with path 40 and row 33. Homogeneous regions of interest (ROI) were chosen and cross-calibration was performed using an image statistics approach to monitor the long-term stability of the two sensors.

Nevada↗

USGS2008

Evaluation of candidate Landsat Data Gap Sensors

The capabilities of the currently operational Landsat satellites may be lost before the launch of the follow-on Landsat Data Continuity Mission (LDCM), thus producing a gap in the Landsat data record and the National Satellite Land Remote Sensing Data Archive (NSLRSDA). In anticipation of a gap, the Federal agencies responsible for Landsat program management, the National Aeronautics and Space Administration (NASA) and the Department of Interior (DOI) U. S. Geological Survey (USGS), convened a Landsat Data Gap Study Team (LDGST). The study team assessed the basic characteristics of multiple systems and identified sensors aboard the China-Brazil Earth Resources Satellite (CBERS-2) and the Indian Remote Sensing (IRS-P6) ResourceSat-1 satellite as the most promising sources of Landsat-like data. The sensors include the combination of CBERS-2 Infrared Multi-spectral Scanner (IRMSS) and High Resolution Charged Coupled Device (CCD), as well as the IRS-P6 Advanced Wide Field Sensor (AWiFS) and the IRS-P6 Linear Imaging Self Scanning Sensor (LISS-III). The study team concluded that more robust technical evaluations of data and sensor performance are required before gap mitigation strategies can be fully formulated. A technical report is made available that summarizes the results from those evaluations, including the initial data characterization and science utility evaluation. The report can be accessed at http://calval.cr.usgs.gov/LDGST.php.

Conference Paper↗

USGS2008

Development of Landsat-5 thematic mapper internal calibrator gain and offset table

The National Landsat Archive Production System (NLAPS) has been the primary processing system for Landsat data since U.S. Geological Survey (USGS) Earth Resources Observation and Science Center (EROS) started archiving Landsat data. NLAPS converts raw satellite data into radiometrically and geometrically calibrated products. NLAPS has historically used the Internal Calibrator (IC) to calibrate the reflective bands of the Landsat-5 Thematic Mapper (TM), even though the lamps in the IC were less stable than the TM detectors, as evidenced by vicarious calibration results. In 2003, a major effort was made to model the actual TM gain change and to update NLAPS to use this model rather than the unstable IC data for radiometric calibration. The model coefficients were revised in 2007 to reflect greater understanding of the changes in the TM responsivity. While the calibration updates are important to users with recently processed data, the processing system no longer calculates the original IC gain or offset. For specific applications, it is useful to have a record of the gain and offset actually applied to the older data. Thus, the NLAPS calibration database was used to generate estimated daily values for the radiometric gain and offset that might have been applied to TM data. This paper discusses the need for and generation of the NLAPS IC gain and offset tables. A companion paper covers the application of and errors associated with using these tables.

Conference Paper↗

USGS2007

Radiometric recalibration procedure for Landsat-5 Thematic Mapper data

The Landsat-5 (L5) satellite was launched on March 01, 1984, with a design life of three years. Incredibly, the L5 Thematic Mapper (TM) has collected data for 23 years. Over this time, the detectors have aged, and its radiometric characteristics have changed since launch. The calibration procedures and parameters have also changed with time. Revised radiometric calibrations have improved the radiometric accuracy of recently processed data; however, users with data that were processed prior to the calibration update do not benefit from the revisions. A procedure has been developed to give users the ability to recalibrate their existing Level 1 (Ll) products without having to purchase reprocessed data from the U.S. Geological Survey (USGS). The accuracy of the recalibration is dependent on the knowledge of the prior calibration applied to the data. The “Work Order” File, included with standard National Land Archive Production System (NLAPS) data products, gives parameters that define the applied calibration. These are the Internal Calibrator (IC) calibration parameters or the default prelaunch calibration, if there were problems with the IC calibration. This paper details the recalibration procedure for data processed using IC, in which users have the Work Order file.

Conference Paper↗

USGS2007

Radiometric calibration status of Landsat-7 and Landsat-5

Launched in April 1999, Landsat-7 ETM+ continues to acquire data globally. The Scan Line Corrector in failure in 2003 has affected ground coverage and the recent switch to Bumper Mode operations in April 2007 has degraded the internal geometric accuracy of the data, but the radiometry has been unaffected. The best of the three on-board calibrators for the reflective bands, the Full Aperture Solar Calibrator, has indicated slow changes in the ETM+, but this is believed to be due to contamination on the panel rather then instrument degradation. The Internal Calibrator lamp 2, though it has not been used regularly throughout the whole mission, indicates smaller changes than the FASC since 2003. The changes indicated by lamp 2 are only statistically significant in band 1, circa 0.3% per year, and may be lamp as opposed to instrument degradations. Regular observations of desert targets in the Saharan and Arabian deserts indicate the no change in the ETM+ reflective band response, though the uncertainty is larger and does not preclude the small changes indicated by lamp 2. The thermal band continues to be stable and well-calibrated since an offset error was corrected in late-2000. Launched in 1984, Landsat-5 TM also continues to acquire global data; though without the benefit of an on-board recorder, data can only be acquired where a ground station is within range. Historically, the calibration of the TM reflective bands has used an onboard calibration system with multiple lamps. The calibration procedure for the TM reflective bands was updated in 2003 based on the best estimate at the time, using only one of the three lamps and a cross-calibration with Landsat-7 ETM+. Since then, the Saharan desert sites have been used to validate this calibration model. Problems were found with the lamp based model of up to 13% in band 1. Using the Saharan data, a new model was developed and implemented in the US processing system in April 2007. The TM thermal band was found to have a calibration offset error of 0.092 W/m 2 sr µm (0.68K at 300K) based on vicarious calibration data between 1999 and 2006. The offset error was corrected in the US processing system on April 2007 for all data acquired since April 1999.

Conference Paper↗

USGS2006

Stability of Landsat-4 thematic mapper outgassing models

Oscillations in radiometric gains of the short wave infrared (SWIR) bands in Landsat-4 (L4) and Landsat-5 (L5) Thematic Mappers (TMs) are observed through an analysis of detector responses to the Internal Calibrator (IC) pulses. The oscillations are believed to be caused by an interference effect due to a contaminant film buildup on the window of the cryogenically cooled dewar that houses these detectors. This process of contamination, referred to as outgassing effects, has been well characterized using an optical thin-film model that relates detector responses to the accumulated film thickness and its growth rate. The current models for L4 TM are based on average detector responses to the second brightest IC lamp and have been derived from three data sets acquired during different times throughout the instrument's lifetime. Unlike in L5 TM outgassing characterization, it was found that the L4 TM responses to all three IC lamps can be used to provide accurate characterization and correction for outgassing effects. The analysis of single detector responses revealed an up to five percent difference in the estimated oscillating periods and also indicated a gradual variation of contaminant growth rate over the focal plane.

Conference Paper↗

USGS2005

Landsat-4 and Landsat-5 thematic mapper band 6 historical performance and calibration

Launched in 1982 and 1984 respectively, the Landsat-4 and -5 Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. However, these sensors and their data products were not subjected to the type of intensive monitoring that has been part of the Landsat-7 system since its launch in 1999. With Landsat-4's 11 year and Landsat-5's 20+ year data record, there is a need to understand the historical behavior of the instruments in order to verify the scientific integrity of the archive and processed products. Performance indicators of the Landsat-4 and -5 thermal bands have recently been extracted from a processing system database allowing for a more complete study of thermal band characteristics and calibration than was previously possible. The database records responses to the internal calibration system, instrument temperatures and applied gains and offsets for each band for every scene processed through the National Landsat Archive Production System (NLAPS). Analysis of this database has allowed for greater understanding of the calibration and improvement in the processing system. This paper will cover the trends in the Landsat-4 and -5 thermal bands, the effect of the changes seen in the trends, and how these trends affect the use of the thermal data.

Conference Paper↗

USGS2005

Improvement in absolute calibration accuracy of Landsat-5 TM with Landsat-7 ETM+ data

The ability to detect and quantify changes in the Earth's environment depends on satellites sensors that can provide calibrated, consistent measurements of Earth's surface features through time. A critical step in this process is to put image data from subsequent generations of sensors onto a common radiometric scale. To evaluate Landsat-5 (L5) Thematic Mapper's (TM) utility in this role, image pairs from the L5 TM and Landsat-7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensors were compared. This approach involves comparison of surface observations based on image statistics from large common areas observed eight days apart by the two sensors. The results indicate a significant improvement in the consistency of L5 TM data with respect to L7 ETM+ data, achieved using a revised Look-Up-Table (LUT) procedure as opposed to the historical Internal Calibrator (IC) procedure previously used in the L5 TM product generation system. The average percent difference in reflectance estimates obtained from the L5 TM agree with those from the L7 ETM+ in the Visible and Near Infrared (VNIR) bands to within four percent and in the Short Wave Infrared (SWIR) bands to within six percent.

Conference Paper↗

USGSDate not supplied

Simulation of the long term radiometric responses of the Terra MODIS and EO-1 ALI using Hyperion spectral responses over Railroad Valley Playa in Nevada (RVPN)

The Earth Observing-1 (EO-1) Hyperion instrument provides 220 spectral bands with wavelengths between 400 and 2500 nm at 30 m spatial resolution, which covers a 7.5 km by 100 km area on the ground. The EO-1 spacecraft has another multispectral sensor called the Advanced Land Imager (ALI), which has 10 spectral bands with wavelengths between 400 and 2350 nm at 30 m spatial resolution. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Terra spacecraft was launched in Dec., 1999, and flies approximately 30 minutes behind EO-1. Nearsimultaneous observations from Terra MODIS, EO-1 ALI and Hyperion over a well characterized Railroad Valley Playa in Nevada (RVPN) target are chosen for this study. A uniform region of interest (ROI) within the playa within latitudes and longitudes of 38.48 and -115.71 to 38.53 and -115.66 was chosen for this analysis. A representation of the ground spectra during every near-simultaneous acquisition of MODIS and ALI is obtained using EO-1 Hyperion data. Using the EO-1 Hyperion derived top-of-atmosphere (TOA) reflectance profile along with the ALI and MODIS relative spectral responses (RSR), simulated reflectance for the matching band pairs is calculated. The Hyperion simulated TOA reflectance results are compared to the measured TOA reflectance trends of ALI and MODIS. The long-term measured versus simulated reflectance results are used to examine the relationships and calibration differences between the ALI and MODIS sensors.

Conference Paper↗