MARS EXPRESS SPICAM DATA FILES Description =========================================================================== Revisions -------------------------------------------------------- 2007-07-25 Updated with new informations in the header 2005 01 21 V016 separate UV and IR description - reberac 2005 01 05 V015 add infrared description - reberac 2004 10 12 V014 complete description dimarellis 2004 09 14 V001 initial dimarellis Purpose This document describes the contents of the UV data files which are delivered in the Spicam UV data set. Introduction =========================================================================== All informations needed to read the UV data file are given. This document is organized as: Introduction UV Data UV detector data Definitions Header description Important notes How to read the UV file =========================================================================== UV DATA =========================================================================== UV detector data: =========================================================================== The UV detector is an intensified CCD. The UV channel of SPICAM is a full UV imaging spectrometer: the spectro-image of the object imaged in the focal plane of the parabolic mirror is formed on the cathode of the image intensifier. However, due to telemetry rate constraints, while one measurement can be obtained each second, only 5 spectra can be transmitted for each 1 s measurement. These spectra may be obtained by some electronic binning of the CCD lines (along the wavelength axis) with various modes. When performing a stellar occultation observation, there is no entrance slit of the spectrometer, the image of the star being a point source which spectrum is dispersed along a line of the CCD. When observing an extended source (dayside nadir viewing, or limb measurements), a slit is mechanically put into place at the focus of the parabolic mirror, which isolates a corresponding FOV. The shape of the slit, perpendicular to the dispersion plane, is composed of two parts: a wide slit (about 500 micron wide) and a narrow slit (50 micron wide). The image of the narrow slit covers CCD lines from 0 to 200, and is used for maximum spectral resolution (1 pixel covers 0.54 nm), while the wide slit is achieving a higher photometric sensitivity, at the expense of a reduced spectral resolution (factor of 10). In the following, we will number the five bands from 1 to 5, bands 1 and 2 being fully on the narrow slit, band 4 and 5 being on the wide slit, and band 3 covering both a part of the narrow slit and a part of the wide slit. The UV data consists of 5 bands selected on the CCD. Each band can be one physical row of the CCD OR several physical rows by on chip binning processing (selectable by telecommand). The position of the first band can be selected by telecommand. These parameters are stored in the data file. See below. Description of the Thomson CCD 7863, physical pixels Row number Meaning ---------- ------- 1 Dummy 2 - 289 288 Photon sensitive rows 290 Dummy For each row n pixel -------- 1 - 7 pixels zero reference level (offset) 8 1 pixel isolation 9 - 392 384 sensitive pixels 393 - 396 4 pixels isolation 397 - 406 10 pixels dark current 407 1 pixel isolation 408 dummy pixel Definitions: =========================================================================== Data file is a binary file Data File collection of data records Data record all data associated with an image (image dimensions are free, so spectra is a one dimension image) data record is identified by an indicator ITYPE The contents of a data record is made of a header followed by 1 to 6 sections. The first section is the image itself in pixel values in ADU. The others sections are optional. Contents: Header 128 (16 bits) integers with LOW octet first Sections : image defined by header (integer numbers) Header description: =========================================================================== Integer rank Name Meaning Value Use ------------ ---- ------- ----- --- 1 Data origin = 0 or 1: on-ground = 2: in-flight 2 Data description = 0: raw data 3 File creation date year 4 month 5 day 6 hour 7 min 8 sec 9 Reserved 10 Reserved 11 UTC board TIME year 12 month 13 day 14 hour 15 minute 16 second 17 fraction (1/100th of sec) 18 - 20 Reserved 21 ITYPE Data identification = 0: ground data = 32: simulated data = 33: 5 lines = 34: superpixel = 35: window 22 Reserved 23 INUM Image number 24 IMAGE imode = 0 25 Word type integer2 (Dos) = 0 26 - 30 Reserved 30 Reserved 31 NREC Section 1 length = 32 = (int(npix/64)+1) 32 - 40 Reserved 41 CODEOP operational code = 98: superpixel = 99: window = 100: 5lines = 101: 5 lines (bin>1) = 102: 5 line (bin progr) 42 TI/10 exposure time UV (* 10 msec) 43 X0 = 0 44 Y0 first band position 45 NCOL number of columns = 408 * 46 NLIG number of bands = 5 * 47 BIN binning 48 GAIN gain = 1 49 NPIX Number of pixels = ncol*nlig 50 TPEL Temperature peltier (hot) 51 TCCD Temperature CCD 52 Mission = 1: Mars express = 2: Venus express 53 BE mode = 0: dummy TC = 1: TestN = 2: TestS = 3: not used = 4: Limb = 5: StarLimb1 = 6: StarLimb2 = 7: StarLimb3 = 8: Nadir1 = 9: Nadir2 = 10: Nadir3 = 11: Align = 12: TiProg = 13: Sun1 = 14: Sun2 = 15: Sun3 54 Sampling period 55 HT UV 56 Slit position = 0: not set = 1: set 57 Peltier activation = 0: off = 1: on 58 Pre-cooling duration (Peltier) 59 Nadir Shutter status= 0: closed = 1: open = 2: opening = 255: unknown 60 Solar Shutter status= 0: closed = 1: open 61 UTC packet generation Time Year 62 Month 63 Day 64 Hour 65 Minute 66 Seconds 67 fraction (1/100th of sec) 68 - 70 Reserved 71 Temperature of = 255: unknown SU TRP1 72 Temperature of = 255: unknown SU TRP2 73 Temperature of Peltier's hot side 74 Temperature of CCD 75 Temperature of num board 76 Temperature of BT board .77 Temperature of solar Shutter .78 Temperature of servitudes board 79 Temperature of HVPS 80 Temperature of Structure 81 Main SPICAM LCL = 255: unknown current 82 Time out counter 83 NACK counter 84 IR channel activation= 0: off = 1: on 85 SOIR channel act = 0: off = 1: on 86 vdds Software used to = 0: vdds produce this file = 1:spi dds2uv0 87 - 99 Reserved 100 Nb of characters stored in next 28 words 101 - 128 comments/complements Important notes: =========================================================================== 0. This file is derived from ESOC DDS telemetry file. ESA packets are open and removed. Only science data are kept. 1. The header contains informations for reading the file, but also complement information as time... 2. To read the file, only the parameters marked (*) are mandatory 3. Pixels values are raw values Temperatures are not calibrated 4. (44) is the position of the first band in physical pixel. Each band is made of one or several physical pixels defined by BIN (47) The position of the second band is Y0 + BIN | ... ---------------------------- [ [ BAND 2 [ ---------------------------- Y1 = Y0 + BIN [ BIN [ BAND 1 [ Y0 ---------------------------- 5. (41) CODEOP defines how the 5 bands are created: Values: 100 each band is one physical CCD row (BIN not significant) 101 each band is several physical CCD rows defined by BIN possible values 2, 4, 8, 16, 32 102 Binning is different for each band (BIN not significant) For 1 to 5, binning is 2, 4, 8, 16, 32 1 st band = 2 physical CCD rows 5 th band = 32 physical CCD rows How to read the UV file: =========================================================================== To read UV data file DO: Open the file Loop Until EOF Read 128 integers (LOW octet first, DOS style) Extract parameters: 31 NREC length of section one (image) = 32 45 NCOL number of columns of the image = 408 46 NLIG number of bands = 5 Read NREC * 128 octets Extract NCOL * NLIG octets and store in array (NCOL, NLIG) ==> Data image is extracted Goto Loop