Landsat 9 is planned for launch in December 2020 to continue the mission of observing changes on the Earth’s surface that began in 1972 with the launch of Landsat 1. Like Landsat 8, Landsat 9 will carry two imaging instruments: Operational Land Imager 2 (OLI-2), designed and built by Ball Aerospace**, and Thermal Infrared Sensor 2 (TIRS-2), manufactured by NASA Goddard Space Flight Center (GSFC). As of this writing, both sensors have completed the instrument-level ground testing and are ready for integration into the spacecraft. Data collected during the pre-launch performance testing are analyzed to assess the usability of responses of the video reference pixels (VRPs) located on the focal planes of OLI-2 and Landsat 8 OLI for more accurate detector bias estimates, develop a methodology to correct for nonlinearities in the OLI-2 response and compare it to the OLI correction approach, and determine the spatial performance of TIRS-2.
KEYWORDS: Earth observing sensors, Sensors, Landsat, Space operations, Calibration, Satellites, Signal to noise ratio, Infrared sensors, Aerospace engineering, Data acquisition
The Landsat Data Continuity Mission (LDCM) with two pushbroom Earth-imaging sensors, the Operational Land Imager (OLI) and the Thermal InfraRed Sensor (TIRS), was launched on February 11, 2013. Its on-orbit check out period or commissioning phase lasted about 90 days. During this phase the spacecraft and its instruments were activated, operationally tested and their performance verified. In addition, during this period, the spacecraft was temporarily placed in an intermediary orbit where it drifted relative to the Landsat-7 spacecraft, providing near simultaneous imaging for about 3 days, allowing data comparison and cross calibration. After this tandem-imaging period, LDCM was raised to its final altitude and placed in the position formerly occupied by Landsat-5, i.e., 8 days out of phase with Landsat-7, with about a 10:10 AM equatorial crossing time. At the end of commissioning, the satellite was transferred to the United States Geological Survey (USGS), officially renamed Landsat-8 and declared operational. Data were made available to the public beginning May 31, 2013. The performance of the satellite and two instruments has generally been excellent as evidenced in the quality of the distributed data products.
The Digital Elevation Model (DEM) extraction process traditionally uses a stereo pair of aerial photographs that are sequentially captured using an airborne metric camera. Standard DEM extraction techniques have been naturally extended to utilize satellite imagery. However, the particular characteristics of satellite imaging can cause difficulties in the DEM extraction process. The ephemeris of the spacecraft during the collects, with respect to the ground test site, is the most important factor in the elevation extraction process. When the angle of separation between the stereo images is small, the extraction process typically produces measurements with low accuracy. A large angle of separation can cause an excessive number of erroneous points in the output DEM. There is also a possibility of having occluded areas in the images when drastic topographic variation is present, making it impossible to calculate elevation in the blind spots. The use of three or more images registered to the same ground area can potentially reduce these problems and improve the accuracy of the extracted DEM. The pointing capability of the Multispectral Thermal Imager (MTI) allows for multiple collects of the same area to be taken from different perspectives. This functionality of MTI makes it a good candidate for the implementation of DEM extraction using multiple images for improved accuracy. This paper describes a project to evaluate this capability and the algorithms used to extract DEMs from multi-look MTI imagery.
The Landsat 7 spacecraft and its Enhanced Thematic Mapper Plus (ETM+) were launched on April 15, 1999. Pre-launch modeling of the ETM+ optical system predicted that modulation transfer function (MTF) performance would change on-orbit. A method was developed to monitor the along-scan MTF performance of the ETM+ sensor system using on-orbit data of the Lake Pontchartrain Causeway in Louisiana. ETM+ image scan lines crossing the bridge were treated as multiple measurements of the target taken at varying sampling phases. These line measurements were interleaved to construct an over-sampled target profile for each ETM+ system transfer function. Model parameters were adjusted to achieve the best fit between the simulated profiles and the image measurements. The ETM+ modulation at the Nyquist frequency and the full width at half maximum of the point spread function were computed from the best-fit system transfer function model. Trending these parameters over time revealed apparent MTF performance degradation, observed mainly in the 15-meter resolution ETM+ panchromatic band. This confirmed the pre-launch model prediction that the panchromatic band was the most sensitive to changes in ETM+ optical performance.
The Landsat 7 Image Assessment System was developed to characterize and calibrate the radiometric and geometric performance of the Landsat 7 Enhanced Thematic Mapper Pius (ETM+) instrument. Algorithms and software assess the geometric performance of the Landsat 7 spacecraft and ETM+ sensor system and perform geometric calibration by estimating sensor and spacecraft geometric parameters. Following the initial on-orbit calibration, performed during the Landsat 7 on- orbit initialization and verification period, all geometric performance goals were met. Geometric characterization and calibration activities will continue for the life of the Landsat 7 mission.
Early in its mission, the Landsat-7 spacecraft was temporarily placed in a “tandem” orbit very close to that of the Landsat-5 spacecraft in order to facilitate the establishment of sensor calibration continuity between the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. The key period for the tandem configuration was June 1-4, 1999, during which hundreds of nearly-coincident matching scenes were recorded by both the Landsat-7 ETM+ and, in cooperation with Space Imaging and international ground stations, the Landsat-5 TM as well. The paper presents a methodology for Landsat-7 ETM+ and Landsat-5 TM cross-calibration and results based on analysis of three tandem image pairs. The approach incorporates adjustments for spectral band differences between the two sensors. With the well- calibrated ETM+ as a reference, the tandem-based cross-calibrations for the three image pairs yield TM responsivities that are consistent to each other to within a few percent or better depending on the spectral band. Comparisons with independent methods and results obtained by other groups indicate that the tandem-based cross-calibration is in close agreement with the independent results in spectral bands 1-3 but compares less favourably in the other bands.
KEYWORDS: Calibration, Sensors, Earth observing sensors, Signal to noise ratio, Landsat, Space operations, Satellites, Lamps, Data centers, Remote sensing
The goal of the current Landsat mission is to acquire annual data sets of optical band digital imagery of the landmass of the Earth. Ground spatial resolutions for the panchromatic, reflective and emissive bands are 15, 30 and 60 meters, respectively. The design life for the Enhanced Thematic Mapper Plus (ETM+) imager on the Landsat-7 satellite is five years. The satellite was launched on April 15, 1999. The mission builds on the 27-year continuous archive of thematic images of the Earth from previous Landsat satellites. Early results from the ETM+ instrument, the spacecraft, and the ground processing indicate that the image quality is as good as expected and all systems are working. Partial Aperture Solar Calibrator (PASC) 100-day radiometric background stability is approximately plus or minus 1.0%. Full Aperture Solar Calibrator (FASC) 2-day stability is approximately plus or minus 0.2%. Mid-scale per pixel noise is approximately plus or minus 1.0%. Operational collection of Landsat's Long Term Acquisition Plan (LTAP) started June 29th. NASA Goddard Space Flight Center (GSFC) is responsible for the instrument, spacecraft, launch, flight operations and science team investigations. On October 1, 2000 USGS EROS Data Center (EDC) takes over flight operations while continuing archiving, monitoring quality, and distributing the imagery without restrictions on reprocessing and redistribution.
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