PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2006-12-27 SOC:Carcich Initial version; " RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "NH" INSTRUMENT_ID = "LEISA" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "LINEAR ETALON IMAGING SPECTRAL ARRAY" INSTRUMENT_TYPE = "INFRARED IMAGING SPECTROMETER" INSTRUMENT_DESC = " ######################################################################## ######################################################################## REQUIRED READING: - Reuter et al. (2007) [REUTERETAL2007] ######################################################################## ######################################################################## The LEISA description was was adapted from Reuter et al. (2007) [REUTERETAL2007], Reuter et al. (2005) [REUTERETAL2005] and the New Horizons website. INSTRUMENT OVERVIEW ======== LEISA is a wedged filter infra-red spectral imager that operates in a push-broom mode. SPECIFICATIONS -------- NAME: LEISA (Note 1) DESCRIPTION: Infrared Imager PRINCIPAL INVESTIGATOR: Alan Stern, SwRI WAVELENGTH RANGE: 1250 - 2500 nm FIELD OF VIEW: 15.9 x 15.9 mRad ANGULAR RESOLUTION: 0.062 mRad WAVELENGTH RESOLUTION: 6.5 nm/pixel (Note 2); 3.7 nm/pixel (Note 3) Note 1: Linear Etalon Imaging Spectral Array Note 2: Full spectral range Note 3: 2100 - 2250 nm DESCRIPTION -------- LEISA operates at infrared wavelengths (it uses heat radiation), and its etalon acts like a prism to bend different wavelengths of light by different amounts so that each wavelength can be analyzed separately. Since different molecules emit and absorb light at different wavelengths, analysis of the different components of the light by LEISA can be used to identify the unique 'fingerprints' of these molecules. LEISA will be used to map the distribution of frosts of methane (CH4), molecular nitrogen (N2), carbon monoxide (CO), and water (H2O) over the surface of Pluto and the water frost distribution over the surface of Charon. LEISA data may also reveal new constituents on the surfaces that have not yet been detected. Scientific Objectives ======== Hemispheric near-infrared spectral maps of Pluto and Charon at best resolution exceeding 10 km/pixel Hemispheric distributions of N2, CO, CH4 on Pluto at a best resolution exceeding 10 km/pixel. Surface temperature mapping of Pluto and Charon hase-angle-dependent spectral maps of Pluto and Charon Calibration ======== See Reuter et al. (2007) sections 5 & Operational Considerations ======== LEISA images a scene through a wedged filter (linear variable filter, Rosenberg et al., 1994) placed about 100 micrometers above a 256x256 pixel Mercury Cadmium Telluride (HgCdTe) detector array (a PICNIC array). An image is formed on both the wedged filter and the array simultaneously (there is less than 5% spectral broadening by the f/8.7 beam). LEISA forms a spectral map by scanning the FOV across the surface in a push broom fashion, similar to that of the MVIC TDI channels. The frame rate is synchronized to the rate of the scan, so that a frame is read out each time the image moves by the single pixel IFOV. The LVF is fabricated such that the wavelength varies along one dimension, the scan direction. Detectors ======== The LEISA detector is a 1.2 to 2.5 micrometer HgCdTe PICNIC array, supplied by Rockwell Scientific Corporation of Camarillo CA. The array is a 256x256 pixel array and each pixel is 40x40 micrometers^2 in area. However, several modifications were made to the standard PICNIC array. The HgCdTe was grown on a CdTe substrate using Molecular Beam Epitaxy (MBE) to provide good lattice matching and low dark currents. The detector was bump bonded to a standard PICNIC multiplexer and the resulting hybrid was mounted to molybdenum pad. This process reduces mechanical stress induced during cooling to operational temperature. It is estimated that the assembly can safely undergo at least 1000 thermal cycles. See Reuter et al. (2007) for more detector details. Electronics ======== See Reuter et al. (2007) section 4.0. Filters ======== The filter, supplied by JDSU Uniphase/ Optical Coating Laboratories Inc. of Santa Rosa CA, was made in two segments. The first, covering from 1.25 to 2.5 micrometers at a constant resolving power (constant delta-lambda/lambda) of about 240, provides information primarily for surface composition mapping. The second, covering from 2.1 to 2.25 micrometers at a constant resolving power of about 560, uses temperature dependent changes in the spectral structure of solid N2 near the alpha to beta transition at 35 K to provide surface temperature maps. In both segments, a constant resolving power is achieved by making the transmitted wavelength depend logarithmically on position. The two segments were bonded together to form a single filter element. This filter was, in turn, bonded into a holder and mounted such that the filter surface is about 100 micrometers above the surface of the array. The refractive index of the array is approximately 2.7 so that the total optical path between the filter and photo-active area of the array is less than 200 micrometers. In this distance, the f/8.7 beam spreads about 0.5 pixel, so when the focus position is optimized between the array and filter surface, the convolved image smear is about 0.04 pixel. Optics ======== See Reuter et al. (2007) section 3. Operational Modes ======== The array readout is performed in Read/Reset pairs. The accumulated charge is read, then the CCD is reset and read immeadiately. After the integration time has expired, the readout cycle is repeated. The difference between the Read value and the previous Reset value is the charge accumulated durring the integration time. LEISA has two recording modes. In the Subtracted mode the Reset value is subtracted from the Read value and the result is recorded. In the Raw mode the Read and Reset values are both recorded. [***N.B. We do not see the fourth axis appear in the single lrw_ image taken so far - Archive team] Prefix for FITS Dimensions of Mode file data FITS file Subtracted lsb_ (256 x 256 x N) Raw lrw_ (256 x 256 x N x 2) N: number of image frames in the observation Measured Parameters ======== Radiance. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "REUTERETAL2007" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "REUTERETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END