The Thermal Infrared Sensor on the Landsat Data Continuity Mission

Abstract

The Landsat Data Continuity Mission ('LDCM), a joint NASA and USGS mission, is scheduled for launch in December, 2012. The LRCM instrument payload will consist of the Operational Land Imager (OLI), provided by Ball Aerospace and Technology Corporation (BATC } under contract to NASA and the Thermal Infrared Sensor (TIRS), provided by NASA's Goddard Space Hight Center (GSFC). This paper outlines the design of the TIRS instrument and gives an example of its application to monitoring water consumption by measuring evapotranspiration.Inter Terms-TIRS, LDCM, evapotranspiration I\TROD[ CT1ONAs is implied in the mission name, one element of the LDCM project is to provide continuity with past Landsat sensors. Another element is to provide improvernents in sensors where possible. The Thematic: Mapper (TM), Enhanced Thematic iMapper (ETXl), and Enhanced Thematic Mapper Plus (ETM-) sensors are good examples of this philosophy as the thermal infrared band improved in spatial resolution from 120 to 60 rn for the single-band, whiskbroom-approach systems (See [2] and references therin). While such data have proved important in providing land-use information, volcanic and lire-monitoring, data, and resource management guidance, a dual-band sensor at lower spatial resolution but with improved sensitivity would maintain continuity and provide valuable data for water resource management and agricultural studies. TIRE on LRCM is a 100 meter (I20 meter requirement) spatial resolution push-broorn imager whose two spectral channels, centered at near I0.8 and 12 microns. split the spectral range of the single TM and ETMt thermal band while still providing thermal band data continuity with previous Landsat missions. The push-broom implementation increases s ystem sensitivity by allowing longer integration times than whiskbroom sensors. The two channels allow the use of the split-window" technique to aid in atmospheric correction. The TIRS focal plane operates near 43 K and consists of three Quantum Well Infrared Photodetector (QWIP) arrays to span the 185 km swath width [5]. Infrared filters are used to define the spectral coverage of the two channels. The imaging telescope is a 4-element refractive leas system. A scene select mechanism (SSIvI ) rotates a scene mirror (SM) to change the field of regard from a nadir Earth view to either an on-board blackbody calibrator or a deep space view. The blackbod y is a full aperture calibrator whose temperature may be varied from 270 to 330 K. Figure I shows a model of the TIRS sensor unit with the major elements identified. TIRS DESIGN OVERVIEWIn a pushbroom instrument, an n row by m column 2..D image of a scene is built-up by concatenating; n successive single rove measurements each containin g m pixels. For TIRS on LDCNI, with its 185 knt swath wilh and 100 meter ground sample distance, a single row consists of 1850 pixels (m-1850). Because the orbital motion of the LDC1.1 spacecraft is about 7 kirtrsec it takes approximatel y 0.01 4 second to move the row by 100 meters, and 70 rows of...

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