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... > Instruments > Earth Remote Sensing Instruments > Passive Remote Sensing > Spectrometers/Radiometers > Imaging Spectrometers/Radiometers > TIR

Preferred term

TIR  

Definition

  • The Thermal Infrared Radiometer (TIR) is one of ASTERs three different subsystems. The TIR subsystem uses a Newtonian catadioptric system with an aspheric primary mirror and lenses for aberration correction. Unlike the VNIR and SWIR telescopes, the telescope of the TIR subsystem is fixed with pointing and scanning done by a mirror. Each band uses 10 Mercury-Cadmium-Telluride (HgCdTe) detectors in a staggered array with optical band-pass filters (Table II) over each detector element. Each detector has its own pre-and post-amplifier for a total of 50. As with the SWIR subsystem, the TIR subsystem uses a mechanical split Stirling cycle cooler for maintaining the detectors at 80K. In this case, since the cooler is fixed, the waste heat it generates is removed using a platform supplied cold plate. The scanning mirror functions both for scanning and pointing. In the scanning mode the mirror oscillates at about 7 Hz. For calibration, the scanning mirror rotates 180 degrees from the nadir position to view an internal black body which can be heated or cooled. The scanning/pointing mirror design precludes a view of cold space, so at any one time only a one point temperature calibration can be effected. The system does contain a temperature controlled and monitored chopper to remove low frequency drift. In flight, a single point calibration is done frequently (e.g., every observation). On a less frequent interval, the black body is cooled or heated (to a maximum temperature of 340K) to provide a multipoint thermal calibration. Facility for electrical calibration of the post-amplifiers is also provided. Another major technical challenge facing the ASTER team was to establish before flight that the elements of the inflight calibration and subsystem design will permit high quality accurate thermal radiometry. For the TIR subsystem, the signal-to-noise can be expressed in terms of an NE delta T. The requirement is that the NE delta T be less than 0.3K for all bands with a design goal of less than 0.2K. The signal reference for NE delta T is a blackbody emitter at 300K. The accuracy requirements on the TIR subsystem are given for each of several brightness temperature ranges as follows: 200 - 240K, 3K; 240 - 270K, 2K; 270 - 340K, 1K; and 340 - 370K, 2K. The total data rate for the TIR subsystem, including supplementary telemetry and engineering telemetry, is 4.2 Mbps. Because the TIR subsystem can return useful data both day and night, the duty cycle for this subsystem has been set at 16%. The cryocooler, like that of the SWIR subsystem, operates with a 100% duty cycle. URL: https://asterweb.jpl.nasa.gov/tir.asp (en)

Broader concept

Change note

  • 2017-12-20 18:08:45.0 [tstevens] Insert Concept add broader relation (TIR [3b2904fa-bc88-4a86-b917-59ea09afdd6f,310487] - Imaging Spectrometers/Radiometers [944b7691-af37-4fb4-9393-c114e7997829,290619]);
  • 2017-12-20 18:09:49.0 [tstevens] insert AltLabel (id: null category: primary text: Thermal Infrared Radiometer language code: en);
  • 2018-01-02 08:39:25.0 [tstevens] insert Definition (id: null text: The Thermal Infrared Radiometer (TIR) is one of ASTERs three different subsystems. The TIR subsystem uses a Newtonian catadioptric system with an aspheric primary mirror and lenses for aberration correction. Unlike the VNIR and SWIR telescopes, the telescope of the TIR subsystem is fixed with pointing and scanning done by a mirror. Each band uses 10 Mercury-Cadmium-Telluride (HgCdTe) detectors in a staggered array with optical band-pass filters (Table II) over each detector element. Each detector has its own pre-and post-amplifier for a total of 50. As with the SWIR subsystem, the TIR subsystem uses a mechanical split Stirling cycle cooler for maintaining the detectors at 80K. In this case, since the cooler is fixed, the waste heat it generates is removed using a platform supplied cold plate. The scanning mirror functions both for scanning and pointing. In the scanning mode the mirror oscillates at about 7 Hz. For calibration, the scanning mirror rotates 180 degrees from the nadir position to view an internal black body which can be heated or cooled. The scanning/pointing mirror design precludes a view of cold space, so at any one time only a one point temperature calibration can be effected. The system does contain a temperature controlled and monitored chopper to remove low frequency drift. In flight, a single point calibration is done frequently (e.g., every observation). On a less frequent interval, the black body is cooled or heated (to a maximum temperature of 340K) to provide a multipoint thermal calibration. Facility for electrical calibration of the post-amplifiers is also provided. Another major technical challenge facing the ASTER team was to establish before flight that the elements of the inflight calibration and subsystem design will permit high quality accurate thermal radiometry. For the TIR subsystem, the signal-to-noise can be expressed in terms of an NE delta T. The requirement is that the NE delta T be less than 0.3K for all bands with a design goal of less than 0.2K. The signal reference for NE delta T is a blackbody emitter at 300K. The accuracy requirements on the TIR subsystem are given for each of several brightness temperature ranges as follows: 200 - 240K, 3K; 240 - 270K, 2K; 270 - 340K, 1K; and 340 - 370K, 2K. The total data rate for the TIR subsystem, including supplementary telemetry and engineering telemetry, is 4.2 Mbps. Because the TIR subsystem can return useful data both day and night, the duty cycle for this subsystem has been set at 16%. The cryocooler, like that of the SWIR subsystem, operates with a 100% duty cycle. URL: https://asterweb.jpl.nasa.gov/tir.asp language code: en);

URI

https://gcmd.earthdata.nasa.gov/kms/concept/3b2904fa-bc88-4a86-b917-59ea09afdd6f

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