Data Set Overview =================== This collection contains image and status data generated by the BOPPS Infra-Red Camera (BIRC) during ground calibration. The image data are separated into three types: Raw - reconstructed from telemetry and saved as FITS files. Each fits file represents a single image frame generated by BIRC. Bias Subtracted - The BIRC camera always generates a bias frame at 3.48 ms integration time with every signal frame at the commanded integration time. The raw images are biased such that larger DN indicates a lower signal strength. Subtracting the signal frame from the bias frame (instead of visa versa) removes the bias contribution to the signal and inverts the DN values such that larger DN now indicates higher signal strength. No further processing is done for this product type. Calibrated Data (in DN) - Bias Subtracted images that have had "hot" pixel and "popcorn" noise replaced by the median value of a 3x3 region centered on the hot pixel. After which a flat field was applied to remove fixed pattern noise. The purpose of the ground calibration altitude chamber test was to characterize the detector response at varying signal levels and develop an algorithm for conversion from DN to electrons – ie. conduct a photon transfer test. Since the images themselves were used to determine the algorithm, archiving Level-1 ground calibration images in units of electrons would not be useful for further calibration analysis. Raw, Bias Subtracted, and Calibrated Data are organized into sets, where 1 set consists of all images that were created by a single command call to an automated command script. The same command script was executed multiple times during the calibration test while conditions in the altitude test chamber were changed to simulate different possible flight conditions. Flat Field data (in DN) - Flat fields were generated by collating Bias Subtracted data products associated with a given observation of a uniform field of view, filter, and integration in time order. The software then removes hot pixels and popcorn noise. The filtered images are then co-added, divided by the number of images co-added, and normalized using the mean value of the averaged image in the 3 arcmin field of view. Status data generated during ground calibration is also contained in this collection: Temperature Data - consisting of ASCII fixed-width tables that contain temperature values reported by sensors in the BIRC instrument. These have been converted from DN to engineering values. Relay Data - consisting of ASCII fixed-width tables that contain information on various relay states and the cryo-cooler pressure. No Pointing data exists for ground calibration because the BIRC instrument was not mounted on the telescope. Finally, the photon transfer test results are stored as a data product in this collection. The SIS document explains the photon transfer test and describes how it was used to generate the DN to electron algorithm. Processing ========== After unpacking the image data from the telemetry files, all bias and signal image pairs are collated. The raw images are biased such that larger DN indicates a lower signal strength. The signal image is subtracted from the bias image to remove the bias contribution to the signal. This also inverts the DN values such that larger DN now indicates higher signal strength. The individual raw images are saved as RAW product files and the bias-subtracted image pairs saved as BIAS_SUBTRACTED product files. Flat fields are then created, with one flat field composed of all images from 10 consecutive sets. This flat field is then applied to all sets which contributed to the flat field generation. Thus, a flat field created from sets 10 - 19 is then applied to the individual sets from 10 to 19. For generation of calibrated images the first step was to remove pixel noise in individual BIAS SUBTRACTED images by using a spatial filter to identify “hot” pixels (pixels that remain at high signal throughout multiple images) and replace them by the median value of a 3x3 pixel region centered on the hot pixel. The next step was to apply a flat field (also in DN) to each image to remove fixed-pattern noise. Temperature and relay data were downloaded from the BIRC instrument and an algorithm was applied to convert the fields from DN to electrons. A photon transfer test was then conducted on the individual sets. Results of the photon transfer test were stored as ASCII files. The SIS describes the photon transfer test and the results which led to the generation of the algorithm to go from DN to electrons. Data ==== Each image product is stored in FITS format in 32-bit floating point datatype. Additional metadata is contained in the XML PDS label assoociated with the FITS files. Each status product and the photon transfer test product is stored in ASCII fixed-width table format. Additional metadata is contained in the XML PDS label associated with the ASCII table file. File Naming Convention ---------------------- RAW, BIAS_SUBTRACTED, CALIBRATED The file naming convention for the raw, bias-subtracted, and calibrated image products in this collection is: obsd_n_hhmmssMSC_F###_YYYYt.ext where: obsd – 4 character string identifying the type of observation. See table 5 in the SIS for a short description of each of the observation types identified. n – single digit indicating filter used. See table 6 in the SIS for a list of filter number vs. wavelength. The filter wavelength is also noted in the XML label. hhmmssMSC – hour, minute, second, millisecond in UTC associated with the read time of the image. F### - the three digit temperature recorded by the window 1 sensor in degrees C rounded to the nearest whole degree. The ‘F’ is either the character ‘p’ or ‘n’ depending on whether the temperature is a positive or negative value. YYYY – the four digit integration time of the image in milliseconds, rounded to the nearest millisecond. t – single character indicating the product type: r - raw image b - bias subtracted image d - calibrated with pixels in units of DN .ext is a three character file extension. Either ‘fit’ for the fits file or ‘xml’ for the PDS4 XML label. FLATFIELD The file naming convention for the flatfield products in this collection is: obsd_x_n_hhmmss_t_YYYY.ext where: obsd – 4 character string identifying the type of observation. See table 5 for a short description of each of the observation types identified x – a digit identifying the shift subset number. n – single digit indicating filter used. See table 6 in the SIS for a list of filter number vs. wavelength. The filter wavelength is also noted in the XML label. hhmmss – two digit hour, two digit minute, two digit second corresponding to the timetag of the first image in the set of images used to generate the product. t – product type f – flat field. Normalized co-added image YYYY – the four digit integration time of the image in milliseconds, rounded to the nearest millisecond. .ext is a three character file extension. Either ‘fit’ for the fits file or ‘xml’ for the PDS4 XML label. An additional reference file ending in ‘txt’ is also created and is referenced by the XML label. This reference file contains the set of images that were used to generate the Level-2 image product. STATUS (RELAY, TEMPERATURE) The file naming convention for the Status data products in this collection is: yyyy_mmdd_hhmmss_obsd_t.ext where: yyyy_mmdd– four digit year, two digit month, two digit day of month corresponding to the timetag of the first record converted to UTC hhmmss – two digit hour, two digit minute, two digit second corresponding to the timetag of the first record converted to UTC obsd – 4 character string identifying the type of observation. See table 5 in the SIS for a short description of each of the observation types identified. t – single character indicating the product type: r – RELAYS t – TEMPERATURE .ext is a three character file extension. Either ‘tab’ for the ASCII table file or ‘xml’ for the PDS4 XML label. PHOTON TRANSFER TEST (PTT) The file naming convention for the photon transfer test in this collection is ptt_setMM_setNN.ext MM – two digit number indicating starting set included in table of results. NN - two digit number indicating ending set included in table of results. .ext is a three character file extension. Either ‘tab’ for the ASCII fixed-width table file or ‘xml’ for the PDS4 XML label. File Organization ----------------- The files are organized according to product type, then by set. Note that the raw and biasSubtracted folders also contain a "ground_cal_pretest" folder. This folder contains image data that was generated before the altitude chamber reached the initial settings required for the test. The images in "ground_cal_pretest" were generated to validate that the BIRC instrument was working properly prior to the start of the test.