Instrument Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument:lwir.clem1::1.0 |
NAME |
LONG WAVELENGTH INFRARED CAMERA |
TYPE |
IMAGER |
DESCRIPTION |
Online Reference: http://wundow.wustl.edu/clbin/clsearch.pl Instrument Overview =================== The Longwave Infrared Camera (LWIR) camera uses a catadioptric lens with a 128 x 128 mercury cadmium telluride (HCT) focal plane array (FPA). The FPA was mechanically cooled to cryogenic temperatures during operation with a temperature set point goal of 65 K. The optics design incorporates an internal relay with 100% cold shield efficiency. Wavelength range was controlled by the cold filter to between 8.0 and 9.5 microns. Camera electronic design is virtually identical to the NIR camera, with a minor alteration in line readout to compensate for the difference in column count between the two arrays (256 for the NIR, 128 for the LWIR). The NIR and LWIR cameras also share a common cryocooler and dewar design, with minor modifications made to accommodate cold shield and cold filter differences. Scientific Objectives ===================== The LWIR camera performed thermal observations of the Lunar surface in the broad-band spectral region centered at 8750 nanometers. Because of the narrow field-of-view of the LWIR camera, overlapping coverage in the cross track-direction was not possible between -80 and +80 degrees of latitude. Calibration =========== The radiometric calibration converts the digitized signal received from the camera (DN value) into a quantity that is proportional to the radiance reaching the sensor. The sensitivity of the CCD focal plane array varies across the field of view. The instrument response is sensitive to the temperatures of the FPA, optics, and cryocooler. During mission operations it was discovered that a sufficient cryocooler cool-down period was needed before temperatures of the instrument became stable. The LWIR camera was calibrated before launch. Laboratory observations of a flat field under various operating temperatures and camera operation modes provide information about the sensitivity of the camera under expected spaceflight conditions. During inflight operations, calibration observations were made over the Apollo 17 Landing site where surface temperatures were measured in-situ. Geometric calibration removes optical distortions of the imaging system. The geometric distortion of the LWIR camera has been shown to be minimal (maximum optical distortion does not exceed 0.1 pixels) and can be satisfactorily modeled by a radially dependent 2nd order polynomial. For additional information of radiometric calibration of the LWIR camera see [LAWSONETAL2000]. Operational Modes ================= The LWIR camera had three operating modes: 1. Four selectable image integration times (0.144, 0.92, 2.30, 4.60 ms) were available, but only 0.144 ms was used. 2. Gain Mode. The gain mode represents the multiplicative constant applied to the image data passing through the A/D converter. There were 32 (5 bit) gain state settings were available. 3. Offset Mode. The offset mode represents the additive constant applied to the image data passing through the A/D converter. There were 256 (8 bit) offset mode settings. Camera Specifications ===================== Detectors --------- Focal Plane Array - Type : Amber PV HgCdTe Pixel format : 128x128 Pixel size : 50x50 microns Non-operable pixels : <5% FPA Operating Temperature: 65 K nominal FPA well capacity : 42 million electrons Field of view : 1 deg. x 1 deg. Pixel IFOV : 143 x 143 microrad Point spread : >60% energy in 79 micrometer slit Electronics ----------- A/D resolution : 8 bits Frame rate : 52.9 Hz (single frame mode) Pixel rate : 500kHz Integration times : 0.144, 0.92, 2.30, and 4.60 ms Digitization gain : 0.5 to 36 X voltage multiplication Offset control : 8 bits Power : 13.0 W Filters ------- No filter wheel housing existed on the LWIR camera. The single spectral band is centered at 8750 nm with a band width of 1500 nm. Optics ------ Equivalent clear aperture : 29nm Effective focal length : 96 mm Cold stop : F/2.67, 7.47 mm diameter Cold shield efficiency : 100% Focal Length : 350 nm Mechanical ---------- Mass : 2100 grams Size : 14.7 cm diameter x 36.1 cm long Subsystems ========== Cryocooler ---------- Type : Ricor K506B integral Stirling with H-10 FPA temperature closed-loop control electronics Avg. power : 11.0 W steady-state |
MODEL IDENTIFIER | |
NAIF INSTRUMENT IDENTIFIER |
not applicable |
SERIAL NUMBER |
not applicable |
REFERENCES |
Lawson, S.L., B.M. Jakosky, H.-S. Park, and M.T. Mellon, Brightness
temperatures of the lunar surface: Calibration and global analysis of the
Clementine long-wave infrared camera data, J. Geophys. Res., 105,
4273-4290, 2000. Priest, R.E., I.T. Lewis, N.R. Sewall, H. Park, M.J. Shannon, A.G. Ledebuhr, L.D. Pleasance, M.A. Massie, and K. Metschuleit, Clementine Longwave Infrared Camera, Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE), 2475, pp. 405-416, 1995. |