Instrument Overview
  ===================
    There are 2 Navigation Cameras (Navcams) on each rover. The Navcams
    are located on the Pancam Mast Assembly (PMA). The Navcams have the
    exact same optical design as the EDLcam and the Hazcams. The Navcams
    are used to acquire images of the terrain and landscape on Mars,
    which can be used to help in the navigation of the rover.
 
    The Navcams are made of a detector head and an electronics box. The
    detector head houses a lens assembly and a Charge Coupled Device
    detector (CCD). The electronics box contains the CCD driver
    electronics, the 12-bit Analog to Digital Converter (ADC),
    camera/rover interface electronics, and a heater resistor that will
    keep the box above the minimum operating temperature of 218 K.
 
    Information in this instrument description is taken from the Mars
    Exploration Rover Engineering Cameras paper[MAKIETAL2003]. See this
    paper for more details.
 
 
  Instrument Objectives
  =====================
    The chief objectives of the Navcams are:
 
    1) to support the operation of the rover on the surface of Mars by
       acquiring images of the terrain and landscape,
 
    2) to acquire images for support of auto-navigation, IDD operations,
       and pointing of the Pancam and Mini-TES,
 
    3) to investigate the landing sites at cm/ pixel resolution,
 
    4) to acquire images of the terrain that will help identify evidence
       of water based on morphology of rocks and soil,
 
    5) to measure the distribution of rocks and soil around the rover as
       it moves from site to site,
 
    6) to calibrate and validate orbital remote sensing data, and
 
    7) to place rock and soil type encountered by the rover in a
       geological context.
 
 
  Calibration
  ===========
    The Navcam has been calibrated over the flight range of
    temperatures. They were all calibrated with respect to: geometric
    flat field response, detector dark current, camera absolute
    responsivity, detector noise performance, and detector gain.
 
 
  Detectors
  =========
    The Navcams use 1024 x 2048-pixel CCD with 12 micron-square pixels
    and a 100% optical fill factor. The CCDs operate in frame-transfer
    mode, dividing the detector into two regions.  One of the regions
    is a 1204 x 1204 pixel photosensitive imaging region where the image
    is recorded. The other region is a 1204 x 1204 shielded storage
    region where the recorded image is shifted and stored during
    detector readout. It takes 5.1 msec to transfer data from the
    imaging region to the storage region, and 5.4 seconds for readout of
    data from the storage region. Each CCD includes 32 non-imaging
    pixels in the serial readout registers, which allow the monitoring
    of the CCD electronics offset and detector noise performance. Both
    the Navcam and Hazcam CCD pixels have full well capacities of
    approximately 160,000 electrons and are digitized at 12 bits/pixel.
    The RMS read noise at cold temperatures (218 K) is approximately 20
    electrons, and the detector systems have gain values of
    approximately 50 e-/DN, which results in a system with approximately
    .5 DN of RMS read noise.
 
    The absolute CCD quantum efficiency (QE) of the CCDs has been
    measured between 400 and 1000 nm at four operating temperatures
    ranging from 218 K and 278 K.  The QE of the MER CCDs is typical
    of a silicon CCD detector, with sensitivity peaking at 700 nm with a
    QE value of approximately 43%. The SNR of the detector system is
    essentially Poisson-limited because of its low readout noise and
    small dark current rates in the Martian operating envirionments.
 
 
  Electronics
  ===========
    The Navcam CCDs use a 'clocked antiblooming' readout technique,
    instead of having anti-blooming circuitry. The proper choice of
    autoexposure parameters prevent the blooming effect.
 
    The Navcams also have the capability for onboard image processing.
    The Navcams can do pixel summation in which they sum the rows and
    columns of an image, returning the results in a one-dimensional
    array of 32-bit integers whose length is the image height. These are
    very useful when the spatial content of an image has relatively low
    scene entropy and the emphasis is on the radiometry. The flight
    software (FSW) can also calculate and return the histogram of an
    image, which can be useful for atmospheric observations. MER images
    can be spatially downsampled to a user-specified image size using
    one of a few techniques; nearest neighbor computation of the mean,
    computation of the mean with outlier rejection, and median
    averaging. The FSW also allows the option to downlink a subframed
    region of an image so full resolution can be downlinked at a lower
    data volume. The FSW is also capable of lossy and lossless
    compression of MER images. The rovers will use a ICER wavelet image
    compressor for the lossy and lossless compression.
 
 
  Filters
  =======
    The Navcams use a combination of three filters (Schott OG590,
    KG5, and ND1.3) to create a red bandpass filter centered at
    650 nm and a FWHM of approximately 140 nm.
 
 
  Optics
  ======
    The Navcams have f/12 cameras with a 14.67 nm focal length. They
    have a 45 x 45 degree field of view, with a 60.7 degree diagonal.
    They have an angular resolution at the center of the field of view
    of .82 mrad/pixel. The field depth of the Navcams ranges from .5
    meters to infinity. The nominal exposure time for a noontime image
    on Mars is approximately .25 seconds. This time is 50 times the
    frame transfer time of 5.1 ms. This ensures that the image signal is
    significantly than the image smear acquired during the frame
    transfer.
 
 
  Location
  ========
    The Navcams are attached to a titanium bracket which is mounted on
    the Pancam Mast Elevation Assembly.