PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " Chris Isbell, 2006-10-10 Lisa Gaddis, 2006-10-10" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = CLEM1 INSTRUMENT_ID = NIR OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "Near InfraRed CAMERA" INSTRUMENT_TYPE = CAMERA INSTRUMENT_DESC = " Instrument Overview =================== The Clementine Near Infrared (NIR) Camera used a catadioptric lens with a 256x256 indium antimonide (InSb) Focal Plane Array (FPA) mechanically cooled to cryogenic temperature. The FPA operated at 70 plus-or-minus 0.5 K at the Moon and showed excellent stability over the more than 500 hours of operation in space. The lens design features all ZnSe refractive elements with a relay to provide an external pupil for 100% efficient cold shielding. This lens design was chosen for image quality and focus stability. Wavelength range was constrained by the optics and the InSb response to somewhat less than 1.0 to 5.5 microns. Six wavebands were selected by a NASA science advisory committee for discriminating among major lunar soil types, all falling well inside this wavelength range. Programmable camera electronics allowed 4 integration times, 5 bits of gain, and 8 bits of offset. Gain states are spaced approximately evenly from 0.5 to 36 factors of voltage multiplication. Offset is subtracted before gain is applied with 0 V to full well range that can be set in 1/255 full well increments. The NIR camera performance specifications are shown below. Scientific Objectives ===================== The primary scientific objective of the UVVIS and NIR imaging instruments was to support lunar mineral mapping investigations. Pole-to-pole NADIR observations with solar phase angles kept to less than 30 degrees at mid-latitudes were the predominant viewing conditions during the two month systematic mapping phase of the mission. The UVVIS and NIR cameras provided nearly 100% coverage of the lunar surface in 11 spectral bands ranging in wavelength from 415 to 2780 nm. Image resolution ranges from about 135 meters/pixel at periselene (-28 degrees south latitude for the first month's observations, +28 degrees the second month) to 400 meters/pixel at the poles. Calibration =========== Radiometric calibration converts the digitized signal received from a camera (‘data number’ or DN value) into a quantity that is proportional to the radiance reaching the sensor. The sensitivity of the NIR CCD FPA varied across the field of view. The instrument response is sensitive to the temperatures of the FPA, optics, and cryocooler. During Clementine mission operations it was discovered that a sufficient cryocooler cool-down period was needed before temperatures of the instrument became stable. NIR images at the start of an observational pass over the Moon just prior to turning on the cryocooler may be difficult to calibrate due to temperature instabilities of the instrument. The NIR camera was calibrated prior to launch. Laboratory observations of a flat field under various operating temperatures and camera operation modes provided information about the sensitivity of the camera under expected spaceflight conditions. Extensive pre-flight calibration data were acquired using an automated calibration facility at Lawrence Livermore National Laboratory (LLNL). In a typical calibration configuration, a sensor was mounted inside an environmental chamber whose temperature was set to -20 to 20 degrees C (the expected operating temperatures for the mission). Depending on the measurement types, the sensors saw either a flat diffused light source or an off-axis collimator with various pinholes as the point source. A custom board controlled the sensor parameters from the host computers; the video signal was acquired using a commercial image processor. During data acquisition many thermal parameters such as FPA and chamber temperatures were monitored and recorded as part of the image structure. The pre-flight calibration measurements included radiometric sensitivity; FPA uniformity; gain and offset scale factors; temporal & spatial noise; dark noise dependence on FPA temperatures, integration times, input voltage levels, spectral response of FPA; optical distortion map; point spread function; electronic warm-up time and cryocooler cool down time. Pre-flight calibration attempted to cover similar light levels expected from the lunar surface and spanning the same camera settings required for lunar mapping. During inflight operations, a variety of calibration observations were made, including Apollo landing site observations where laboratory spectra of returned lunar samples have been measured. These data (especially those for the Apollo 16 highlands soils) were used to calibrate the first four filters of the NIR data. The longest NIR wavelengths (2600 and 2780 nm bands) were not normalized to these soil measurements because reflectance information was not available and may be complicated by the presence of thermal emission signatures at longer wavelengths. Before radiometric processing of the NIR data began, two effects specific to the NIR data were characterized: 1) instrument operating modes and 2) instrument thermal background changes during an orbital observation pass over the Moon. The goal of the first characterization was to determine an optimum set of calibration constants to minimize the difference between calibrated values for portions of the Moon imaged sequentially with different camera settings. The goal of the second characterization step was to isolate the thermal background changes during an orbital pass and to define a set of corrections for each orbit. Compensation for these two effects was incorporated into the radiometric calibration steps, and residual effects were removed in later processing. To facilitate creation of NIR mosaics with uniform scene brightness, a photometric normalization procedure was applied to the individual NIR images. The data were normalized to R30, the reflectance expected at an incidence angle (i) and phase angle (p) of 30.0 degrees and an emission angle (e) of 0.0 degrees matching the photometric geometry of lunar samples measured at the reflectance laboratory at Brown University. In addition to this 'standard' radiometric and photometric processing of the Clementine NIR data, empirically derived frame offset corrections were applied to reduce observed residual variations across camera modes and adjacent orbits in the NIR mosaics. Geometric calibration removes optical distortions of the imaging system. The geometric distortion of the NIR camera has been shown to be minimal (maximum optical distortion does not exceed 3.0 pixels) and can be satisfactorily modeled by a 2nd order polynomial. For additional information on the geometric and radiometric calibration of the Clementine imaging systems, please review the volinfo.txt document (and references therein) and/or contact the PDS Imaging Node. Operational Considerations ========================== The pole-to-pole lunar observations provided scenes with a broad range of viewing conditions, ranging from bright observations near zero phase angle at the equator to very low light-level observations at the poles. To properly record an observation with an optimal signal-to-noise ratio it is important to adequately fill the 8-bit (255 levels) dynamic range of the A/D camera output. The integration time (exposure time) and the gain and offset operating modes of the instrument were adjusted to properly record each image. Lunar observations were broken into 10 latitude bins. Each latitude bin contained fixed gain and offset modes and integration times for each camera/filter combination. The Clementine orbit was designed to provide overlapping coverage in both the down-track (~15% overlap) and cross-track (~10% overlap at the equator) directions. The image overlap is necessary to geometrically control images in cartographic applications. Operational Modes ================= The NIR camera had three operating modes: 1. Four selectable image integration times (11, 33, 57, 95 ms). 2. Gain Mode. The gain mode represents the multiplicative constant applied to the image data passing through the A/D converter. Thirty two (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 : PV InSb (Amber) Pixel format : 256 x 256 Pixel size : 38 x 38 microns Non-operable pixels : less than 0.5% FPA operating temp. : 70 K FPA well capacity : 11.7 million electrons Field of view : 5.6 deg. x 5.6 deg. Pixel IFOV : 400 x 400 microradians Point spread : greater than 50% energy in 30 function micrometer slit Electronics ----------- A/D resolution : 8 bits Frame rate : 7.1 Hz (single frame mode) Integration times : 11, 33, 57, and 95 ms Digitization gain : 0.5 to 36 X voltage multiplication Offset control : 8 bits Power : 13.0 W Filters ------- Filter Wheel Spectral Position Band --------------------------------------------- A : 1100 nm (plus-or-minus 30 nm) B : 1250 nm (plus-or-minus 30 nm) C : 1500 nm (plus-or-minus 30 nm) D : 2000 nm (plus-or-minus 30 nm) E : 2600 nm (plus-or-minus 30 nm) F : 2780* nm (plus-or-minus 60 nm) * Note that the wavelength of NIR filter F (band 6) has been reported as 2690 nm in places, but that value is the cuton wavelength of the band 6 filter. 2780 nm is the more accurate wavelength of the center of NIR band 6. Optics ------ Clear aperture : 29 nm Effective focal length : 96 mm Cold stop : F/3.33, 6.0 mm diameter Cold shield efficiency : 100% Mechanical ---------- Mass : 1920 grams Size : 10.4 cm x 11.5 cm x 36.5 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 " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "PRIESTETAL1995A" REFERENCE_KEY_ID = "NOZETTEETAL1994" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END