Data Set Overview =================== This collection contains raw images generated by the BOPPS Infra-Red Camera (BIRC) during flight. The BOPPS Infrared Camera (BIRC) is a multispectral infrared imager designed to operate in 8 wavelengths between 2.5 and 5.0 μm, with each spectral width being ~ 3% of the center wavelength, and the astronomical R-band near 640 nm. BIRC was designed to measure the water and CO2 emissions from comets at 2.73 and 4.3 μm, respectively, and the water related infrared absorption feature in asteroids and the Moon from ~ 2.5 to 3.2 μm. This capability is obtained with a Teledyne H2RG cryocooled HgCdTe detector and an 80 cm telescope. The system produces an f/4 image over a field of view of 3 arcminutes, which subtends approximately 151 pixels on the 2K x 2K array, and employs shift/co-add algorithms to increase signal-to-noise for the observation of dim objects. The BIRC is comprised of two subsystems, a collimator and a camera, which are designed to relay the primary image from the 80 cm telescope to the focal plane of the Teledyne H2RG after passing a collimated beam through the cryogenically cooled nine-position filter wheel. The primary image propagates through a CaF2 window on a ‘cold box’ that contains the collimating optics. This subsystem consists of an enclosed cooled, nitrogen-purged box with a collimating mirror and three fold mirrors, all of which are coated with protected gold to reduce thermal self emission. Upon exiting the box, the collimated beam passes through another CaF2 window between it and the evacuated, cryogenically cooled nine-position filter wheel and then into a camera subassembly where the final image is formed on the detector via a small Ritchey-Critean telescope. Custom firmware provided by Teledyne Imaging Systems allows the BIRC flight software to readout a programmable area of interest, which was then defined to be the central 320 x 200 pixel region that contains the 3 arcmin field of view. It is this subframe that is generated by the BIRC instrument for all the image data. The detector performs a 'non-destructive' read of the data in time units of 3.48ms, such that the integration time for an individual image is N * 3.48ms. For any commanded integration time the detector performs two reads. The first read is after 3.48ms, for which the bias image is generated. The second read is at N * 3.48ms, for which the signal image is generated. Processing ========== The RAW images are extracted from BIRC raw telemetry files. The image data in the telemetry files are stored as 12-bit packed integers. Each image is unpacked into a 320 x 200 16-bit integer array and then saved in FITS file format as a 32-bit floating point datatype. These are the products contained in this collection. Pointing and temperature metadata are first-order interpolated to the readtime of the image and stored in the XML label associated with each image. Data ==== FITS Images and PDS Labels -------------------------- Each raw BIRC image is stored in FITS file format with minimal FITS headers. Any associated metadata is contained in the XML PDS label associated with the FITS file. File Naming Convention ---------------------- The file naming convention for a RAW data product 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. In this case: r – RAW .ext is a three character file extension. Either ‘fit’ for the fits file or ‘xml’ for the PDS4 XML label. File Organization ----------------- The files are organized by target, then by operation being performed on the target. Target names are PDS compliant names for the celestial objects being observed. The operation performed commonly falls into one of three categories: -target_search - telescope was slewed to the target while real-time images were generated by the BIRC instrument. Used to verify bright objects, such as calibration stars, were in the field of view. Also used to try and verify dim objects, such as comets, although these were usually only seen after shifting and coadding. There are two types of target search: realtime and shiftadd. Realtime target searches consist of BIRC image data generated at commanded intervals and downloaded in real-time during the mission then displayed on a monitor. Shiftadd target searches consisted of several images generated in quick succession that were then downloaded to be shifted and added in near-realtime to verify the target in the field of view. -H2O - telescope pointed at a fixed RA, DEC while BIRC camera cycles through filters used to detect water vapor emissions. Namely, filters with bands centered at 2.73, 2.45, 3.2, and 3.05 microns. For most targets there are two sets H2O observations, set A and set B. The difference is that the telescope elevation has changed by a commanded number of arcseconds, referred to as "nodding" the telescope. In the case of target HD 163761 only set A was collected, due to time constraints on the mission. -CO2 - telescope pointed at a fixed RA, DEC while BIRC camera cycles through filters used to characterize Co2 features in comets or in surfaces of asteroids. Namely, filters with bands centered at 4.27 and 4.6 microns. For most targets there are two sets of Co2 observations, set A and set B. The difference is that the telescope elevation has changed by a commanded number of arcseconds, referred to as "nodding" the telescope. In the case of target C/2014 E2 there was a third set, set C, which was taken just before the end of the mission. The exceptions are for targets early in flight, during which the instrument took images to perform checkout tests, alignment tests, and focus sweeps. The subfolder name indicates which kinds of tests were performed.