KPL/IK Deep Impact Medium Resolution Imager Instrument kernel =========================================================================== This instrument kernel (I-kernel) contains optics and detector geometric parameters of the Medium Resolution Imager (MRI) instrument mounted on the Deep Impact Flyby (DIF) spacecraft. Version and Date --------------------------------------------------------------------------- Version 1.1 -- July 9, 2019 -- Boris Semenov, NAIF/JPL Changed CCD size to 1024x1024 and CCD center to 512.5,512.5. Version 1.0 -- September 13, 2005 -- Boris Semenov, NAIF/JPL Completed various sections including instrument overview, nominal parameters, frame-detector relationship diagram, optical distortion, etc. INS-*_CENTER keywords were replaced with INS-*_CCD_CENTER. Version 0.1 -- December 20, 2004 -- Boris Semenov, NAIF/JPL Re-defined FOVs using ``angular extent'' style and made FOV angular extents consistent with updated frame definitions. Version 0.0 -- April 13, 2001 -- Boris Semenov, NAIF/JPL Preliminary Version: --- TO BE USED ONLY FOR SOA TOOL DEMONSTRATION --- This version is based solely on [4], which, as of Rev 010216, did NOT contain complete set of information required to understand and define Deep Impact MRI Instrument parameters. Therefore, most of the sections of this IK file either contain target design values or no values at all (just place-holders identifying what items may be included later.) References --------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``C-kernel Required Reading'' 3. Deep Impact Frames Kernel, latest version 4. ``Deep Impact Instruments Requirements Specification'', 2001 February 16, M. Ensminger 5. ``Cassini ISS Geometric Calibration of April 2003'', W. M. Owen, Jr., May 9, 2003 6. E-mails providing DI camera distortion model parameters from Nick Mastrodemos, DI OPNAV team, 04/29/05 and 09/09/05 7. MRI description from the Deep Impact Project public Web site: http://deepimpact.jpl.nasa.gov/tech/mri.html Implementation Notes -------------------------------------------------------- User programs that need I-kernel data must `load' the I-kernel file, normally during program initialization. Loading the kernel using SPICELIB routine FURNSH causes the data items and their associated values present in the kernel to become associated with a data structure called the ``kernel pool''. Then a user's program can obtain the value(s) for any data item using the SPICELIB routines GDPOOL, GIPOOL and GCPOOL. See [1] for details. This file was created and can be updated with a text editor or word processor. Naming Conventions -------------------------------------------------------- All names referencing values in this I-kernel start with the characters ``INS'' followed by the NAIF DIF spacecraft ID number (-140) followed by the NAIF three digit MRI instrument reference number (200). The remainder of the name is an underscore character followed by the unique name of the data item. For example, the focal length of the MRI camera is specified by INS-140200_FOCAL_LENGTH The upper bound on the length of the name of any data item is 32 characters. If the same item is included in more then one file, or if the same item appears more than once within a single file, the latest value supersedes any earlier values. MRI Overview -------------------------------------------------------- From [7]: "The Medium Resolution Instrument (MRI) serves as the functional backup for the (HRI) and takes images with a scale of 10 m per pixel in the visible spectrum at 700 km. It also provides science context, ejecta imaging, and targeting in visible wavelengths. The MRI visible field of view covers 1.2 times the expected diameter of the comet's nucleus at closest approach, about 7m per pixel. Unlike the HRI's narrow field of view which is needed for high resolution, the MRI's wider field of view allows it to provide the context of the whole nucleus from different directions when HRI can only see a small part of the nucleus. The wider field of view also allows it to better view the stars and navigate through the gas and dust particles that surround the comet, especially during the last 10 days' approach to the comet. The MRI telescope is a Cassegrain design with a 12 cm aperture and a 2.1 m focal length. The optics, mounts, and baffle tube are of similar construction to the HRI telescope. The MRI and the Impactor Targeting Sensor are identical other than the filter wheel." MRI Mounting Alignment -------------------------------------------------------- Refer to the latest version of Deep Impact Frames Definition Kernel ([3]) for the MRI frame definition and mounting alignment information. MRI Optics Parameters -------------------------------------------------------- The following nominal MRI first order optical parameters are provided in [4]: ------------------------------------------------- parameter value ------------------------------------------------- Focal Length, mm 2100 f/ratio 17.5 FOV Angular Size, milliradians 10.0 x 10.0 IFOV, microradians/pixel 10 ------------------------------------------------- The values in the keywords are given in the same units as in the table above except for angles which are given in radians. \begindata INS-140200_FOCAL_LENGTH = ( 2100.0 ) INS-140200_F/RATIO = ( 17.5 ) INS-140200_FOV_ANGULAR_SIZE = ( 0.01, 0.01 ) INS-140200_IFOV = ( 0.00001, 0.00001 ) \begintext MRI FOV Definition --------------------------------------------------------------------------- MRI FOV defined in this section is based on the MRI detector FOV angular size provided in the Table in "MRI Optics Parameters" section above. The set of keywords in the following data section defines nominal MRI FOV with respect to the DIF_MRI frame to be a rectangle with angular size of 10.0 by 10.0 milliradians centered about the boresight vector along +Z axis of DIF_MRI frame. \begindata INS-140200_FOV_FRAME = 'DIF_MRI' INS-140200_FOV_SHAPE = 'RECTANGLE' INS-140200_BORESIGHT = ( 0.0000000000000000 0.0000000000000000 +1.0000000000000000 ) INS-140200_FOV_CLASS_SPEC = 'ANGLES' INS-140200_FOV_REF_VECTOR = ( 0.0000000000000000 +1.0000000000000000 0.0000000000000000 ) INS-140200_FOV_REF_ANGLE = ( 0.005 ) INS-140200_FOV_CROSS_ANGLE = ( 0.005 ) INS-140200_FOV_ANGLE_UNITS = 'RADIANS' \begintext MRI Optical Distortion Specification -------------------------------------------------------- The following distortion model has been used by the DI OPNAV team for this camera during the mission (based on [5]; according to Bill Owen DI OPNAV used the same camera model as Cassini OPNAV): A 3d vector (P) in the camera frame is mapped into sample and line (S,L) coordinates by: ( X ) FL ( P(1) ) ( ) = ------ ( ) ( Y ) P(3) ( P(2) ) 2 2 2 R = X + Y ( dX ) ( X*R*R X*Y X*X ) ( E2 ) ( ) = ( ) ( E5 ) ( dY ) ( Y*R*R Y*Y X*Y ) ( E6 ) ( S ) ( Kx Kxy ) ( X + dX ) ( S0 ) ( ) = ( ) ( ) + ( ) ( L ) ( Kyx Ky ) ( Y + dY ) ( L0 ) where FL is the camera focal length in mm; the E(i) are coefficients of the cubic radial distortion and detector misalignment; the matrix K maps millimeters to pixels in the focal plane; and (S0,L0) are the focal plane coordinates of the optical axis. The following MRI optical distortion parameters for this model were provided by Nick Mastrodemos, DI OPNAV ([6]): FL = 2101.0915 KMAT(1,1) = 4.76190E+01 KMAT(2,2) = -4.76317E+01 KMAT(2,1) = -1.67302E-03 EM(2) = 7.39951E-07 EM(5) = -3.66104E-06 EM(6) = -1.15820E-05 This data is provided in the data block below. Note the change of the sign -- from "-" to "+" -- of the Ky (KMAT(2,2)) element provided in the corresponding keyword. This change is needed to make the model apply to the raw MRI images ``flipped'' about the vertical centerline rather than to ``as is'' raw MRI images. \begindata INS-140200_FOCAL_LENGTH = 2101.0915 INS-140200_KMAT = ( 4.76190E+01, -1.67302E-03, 0.0, 4.76317E+01 ) INS-140200_EM = ( 7.39951E-07, -3.66104E-06, -1.15820E-05 ) INS-140200_CCD_CENTER = ( 512.5, 512.5 ) \begintext This small fragment of SPICE-based FORTRAN code illustrated how these parameters can be loaded into an application and used to compute sample and line (not of a raw MRI image but of an raw MRI image ``flipped'' about vertical centerline) for a 3d vector defined in the camera frame, DIF_MRI: C C Retrieve loaded camera distortion parameters. C CALL GDPOOL ( 'INS-140200_FOCAL_LENGTH', 1, 1, N, FL, FND1 ) CALL GDPOOL ( 'INS-140200_KMAT', 1, 4, N, KMAT, FND2 ) CALL GDPOOL ( 'INS-140200_EM', 1, 3, N, EM, FND3 ) CALL GDPOOL ( 'INS-140200_CCD_CENTER', 1, 2, N, CNTR, FND4 ) C C Given 3d vector VECTOR in the camera frame, 'DIF_MRI', C compute ideal X and Y in sample/line space. C CALL VSCLG ( FL / VECTOR(3), VECTOR, 2, XYIDL ) C C Construct XYR2 matrix. C R2 = XYIDL(1)**2 + XYIDL(2)**2 XYRMAT(1,1) = XYIDL(1) * R2 XYRMAT(2,1) = XYIDL(2) * R2 XYRMAT(1,2) = XYIDL(1) * XYIDL(2) XYRMAT(2,2) = XYIDL(2) * XYIDL(2) XYRMAT(1,3) = XYIDL(1) * XYIDL(1) XYRMAT(2,3) = XYIDL(1) * XYIDL(2) C C Compute delta X and Y. C CALL MXVG ( XYRMAT, EM, 2, 3, XYDLT ) C C Compute line sample, SL (sample is the first element, C line is the second element) in the raw MRI image C ``flipped'' about vertical centerline, corresponding C to the input view vector. C CALL VADDG( XYIDL, XYDLT, 2, XY ) CALL MXVG ( KMAT, XY, 2, 2, SLREL ) CALL VADDG( SLREL, CNTR, 2, SL ) MRI Detector Parameters -------------------------------------------------------- The following nominal MRI detector geometry parameters are provided in [4]: ----------------------------------------------- parameter value ----------------------------------------------- Pixel size, microns 21 (a) Number of pixels/mm 47.61904762 (a) Detector Size (physical) 1024 by 1024 Detector Array Center 512.5, 512.5 ----------------------------------------------- (a) Nominal pixel size and number of pixels per mm were computed from the nominal focal length and IFOV provided in the ``MRI Optics Parameters'' section of this file. The values in the keywords are given in the same units as in the table above. \begindata INS-140200_PIXEL_SIZE = ( 21.0 ) INS-140200_K = ( 47.61904762 ) INS-140200_PIXEL_SAMPLES = ( 1024 ) INS-140200_PIXEL_LINES = ( 1024 ) INS-140200_CCD_CENTER = ( 512.5, 512.5 ) \begintext Relationship Between MRI Reference Frame, FOV, and Line/Sample Coordinates --------------------------------------------------------------------------- MRI ``apparent'' FOV with respect to the ``DIF_MRI'' frame (shown line and sample coordinates are NOT for the raw MRI image; they are for the raw MRI image ``flipped'' about vertical centerline): 1024 pixels/line Line 1, Pixel 1 Line 1, Pixel 1024 --- *-------------------* ^ | | | | | | | | | | +Zmri | | 10.0 mrad | x-------------> +Xmri | | | | | 1024 | | | | lines | | | V | | | --- +---------|---------* | Line 1024, Pixel 1024 | +Ymri V | 10.0 mrad | Boresight (+Z axis) |<----------------->| is into the page | | Platform ID --------------------------------------------------------------------------- This number is the NAIF instrument ID of the platform on which the camera is mounted. For MRI such platform is the spacecraft itself. \begindata INS-140200_PLATFORM_ID = ( -140000 ) \begintext