PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " CHRIS ISBELL AND ERIC ELIASON, 1999-08-05" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = CLEM1 INSTRUMENT_ID = UVVIS OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "ULTRAVIOLET/VISIBLE CAMERA" INSTRUMENT_TYPE = CAMERA INSTRUMENT_DESC = " Instrument Overview =================== The Ultraviolet/Visible Camera (UVVIS) has a catadioptic telescope using fused silica lenses focused onto a metachrome-coated charge couple device (CCD) imager. Active wavelength response is limited on the short wavelength end by the transmission of fused silica and the optical blur of the lens. Wavelength response on the long end is limited by the response of the CCD. Six spectral bands can be selected from a filter wheel which is controlled through the same serial-addressable synchronous interface (SASI). The Thomson focal plane array (FPA) used is a frame-transfer device, accomplishing electronic shuttering by rapidly shifting the active pixel area into the storage area, pausing for the 13-bit programmable shuttering system integration time, then rapidly shifting the captured image into a storage buffer from which the image is read out. Post-FPA electronics allow three gain states followed by 5 bits of offset that span 248 counts in the analog regime to augment the basic 8-bit analog/digital (A/D) conversion. Gain is A/D digitization noise limited, so proper exposure is critical. Working against the day side of the Moon as a target, typical integration times were as short as several milliseconds in the lowest gain state (1000 electrons/bit) near sub-solar illumination points at the brighter spectral bands, increasing to 40 msec near the polar regions in the mid-gain setting for the weaker 415 and 1000 nanometers (nm) spectral bands. The UVVIS performance specifications are shown below. Scientific Objectives ===================== The primary scientific objective of the UVVIS imaging instrument 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 100% coverage of the lunar surface in 11 spectral bands ranging in wavelength from 415 to 2690 nm. Image resolution ranges from 100 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 =========== 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 but appears to be time invariant during the two month lunar observation period. The UVVIS camera was calibrated before launch. Laboratory observations of a flat field under various operating temperatures and camera operation modes provides information about the sensitivity of the camera under expected spaceflight conditions. During inflight operations, a variety of calibration observations were made including images of stars with known radiance (Vega) and the Apollo Landing sites where laboratory spectra of returned lunar samples have been measured. Geometric calibration removes optical distortions of the imaging system. The geometric distortion of the UVVIS 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 on the geometric and radiometric calibration of the Clementine imaging systems, 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. In order 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 settings of the instrument were adjusted to properly record each image. During the systematic mapping, the gain state of the camera was normally set to 1 for the mid-latitude observations and set to 2 (thereby increasing the sensitivity of the A/D converter) at the higher latitudes. Integration times were increased as observations approached the poles. 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. For the UVVIS camera two observations were made in rapid succession acquiring both high and low integration-time images for the same scene. The multiple integration-time imaging was designed to optimally record both maria materials (dark albedo material optimally recorded by the high integration-time image) and highland materials (high albedo materials optimally recorded by the low integration-time image). 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 UVVIS camera had three operating modes: 1. 13-bit programmable integration time. The range of integration times (in microseconds) is given by: Integration Time = [(N+3)*94.5 - 45, N=0,2,3...2**13)]. 2. Gain Mode. The gain mode represents the multiplicative constant applied to the image data passing through the A/D converter. Three gain state settings were available (1,2,4) although gain setting 4 was seldom used during lunar observations. 3. Offset Mode. The offset mode represents the additive constant applied to the image data passing through the A/D converter. There were 14 offset mode settings (1-14) although offset modes 1 and 6 were predominantly used during systematic lunar observations. Camera Specifications ===================== Detectors --------- Thomson Focal Plane Array Type : Si Charge Coupled Device Thomson TH7863-CRU-UV Pixel format : 288x384 Pixel size : 23x23 microns Readout rate : 4MHz Wavelength Sensitivity : 0.3 to 1.1 microns Field of view : 4.2 deg. x 5.6 deg. Pixel IFOV : 255 microradians Point spread : 1.1 to 1.5 pixels Electronics ----------- A/D resolution : 8 bits Frame rate : 10 Hz Readout time : 27.4 msec Integration time : 0.2-733 msec Digitization gain: 150,350,1000 electrons/count Offset control : 248 gray levels Power : 4.5 W Filters ------- Filter Wheel Spectral Position Band ----------------------------------------------- A : 415nm (plus-or-minus 20 nm bw) B : 750nm (plus-or-minus 5) C : 900nm (plus-or-minus 10) D : 950nm (plus-or-minus 15) E : 1000nm (plus-or-minus 15) F : 400 to 950nm broad band Optics ------ Clear aperture : 46nm Speed : F/1.96 Mechanical ---------- Mass : 410 grams Size : 15.5cm x 11.7 cm x 10.4 cm Filter Wheel System - Type : 6 position, 90 deg. stepper motor driven, Hall Effect Position Sensors - Step and Settle time : <250ms Position repeatability : 10mr Power : 0.15 W quiescent, 11.0 W stepping " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KORDASETAL1995" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END