Dataset overview  :  Framing Camera 1 is one of two identical units flying on Dawn  spacecraft. This dataset includes the Reduced Data Record (RDR) version  of all available images acquired during the initial checkout and  pre-Vesta cruise phases (Checkout, Earth to Mars, and Mars to Vesta).  As in the original Raw data sets, in addition to the imagery, ancillary  information is stored within the image headers, as well as a detailed  account of all the reference files used for the calibration. Calibration files needed for further processing are archived as a separate data set. The images in this dataset have been radiometrically calibrated by means of fully reversible procedures, transforming the value of the pixels  from digital units to applicable engineering units without modification  of the geometry.   For more information on the contents and organization of the volume  set refer to the aareadme.txt file located in the root directory of  the data volumes.   Parameters  :   Compression: FC images may optionally be compressed by wavelet  transformation.   Wavelet compression: Images may be integer or floating point wavelet  transform-compressed in the DPU. The integer approach produces lossless  compression, while the floating point can induce distortions of +/-1 DN. The encoding of the wavelets ensures that any length of the data  starting at the beginning can be decoded, thus allowing to compress  further by discarding the trailing part.   Windowing: In order to manage downlink resources, up to 10 portions  of the image can be selected in the DPU and downlinked as subframes.  The subframes are allowed to overlap. During EDR construction each  subframe is stored separately and also mosaicked into the original  image.   Exposure Control: The exposure time of FC images is set  by command for each image.   Pointing: The Framing Cameras are fixed mounted onto the Dawn Instrument deck, with the nominal alignment of the optical axis with the +Z axis of the spacecraft. Deviations from the nominal are documented in the  calibration data.   Filter selection: The FC has 8 filters at its disposal, numbered from F1 to F8. F1 is a broadband (clear) filter, sensitive in the wavelength  interval from 400 to 1100 nm peaking at 700 nm. The narrow-band color  filters are of the interference type, and have wavelengths ranging from  430 to 980 nm.   Processing  :  An FC image downlinked by the spacecraft unpacks into a succession of  one or more compressed image subframes with an attached PDS headers  containing housekeeping items that include full status of the instrument hardware, software configuration, temperature, voltage and current  readings.   The data in one EDR consists of one or more reconstructed image frames,  with the accompanying header translated into text format in the label.  The dimensions and location (pixel coordinates) of each frame are  included for proper further processing. Each frame is formatted into  one file (suffix *.IMG), with an attached label.   Subframes are retained as separate entities and also are reassembled  into their original coordinates in the 'summary' image. Parts of the  reconstructed image not included in the subframes are given a value  of zero.   The label contains all relevant housekeeping information in calibrated  form (e.g. degrees Celsius, volts, or amperes.   For further details on the layout of the data and the possible  combinations of frames, please refer to the Software Interface  Specification.   The calibration process is divided into several steps that aim to remove the effect of different source of noise: conversion from 16-bit integer  to 32-bit floating point, read-out bias, dark current, read-out smear,  flat field non-uniformity, correction of under-sensitive pixels,  exposure normalization, radiometric calibration.   For more detailed information on the calibration process, please refer  to [SCHROEDER&GUTIER2011]. For a discussion of which calibration  images to use for a given activity, please refer to the data set catalog file for DAWN-CAL-FC1-2-EDR-CALIB-IMAGES-V1.0.

Exposure times  :  Due to an idiosyncrasy of the proximity electronics, that takes  approximately 193 milliseconds from the commanding of the image  acquisition to the actual start of the exposure, the images report the  commanding time and the end of exposure. This results in a difference of 193 milliseconds between the usual calculation of exposure time  (STOP_TIME - START_TIME) and the reported EXPOSURE_DURATION, which is  always shorter than the difference of the other two.   Calibration files  :  All the files involved in the calibration of this data set have been  subsequently delivered as part of the calibration data set. Furthermore, the history part of the PDS header of each image lists which calibration files was used for each of the calibration steps.  All the files delivered in the calibration data set are final. Even if  images acquired later in time will require a different calibration file, this will be added to the data set but not replace the old one.