Robotic Arm Camera (RAC) data sets

Data Set Overview

There are multiple methods of performing radiometric correction, distinguished by the RADIOMETRIC_CORRECTION_TYPE keyword. The most common are TAMCAL, RACCAL, MIPLRAD, MIPLRAD2, and MIPLRAD3.

1. Radiance-calibrated RDRs ('RAD', 'RAL')

The non-linearized RDRs are generated from EDRs. They have all of the major instrumental/environmental calibrations applied, such as bias removal, dark current removal, electronic shutter smear effect removal, flat field correction, and bad pixel repair. Then they have been scaled to absolute radiance units using pre-flight radiometric calibration coefficients. The units on these files are (W/m^2/nm/sr).

2. RACCAL Method (RAC Team)

This refers to radiometric correction of RAC and OM instrument data only, performed by the RAC instrument team (MPS) using the RACCAL software suite. It is the most precise correction method applicable to RAC and OM data.

The RAC/OM calibration steps performed by the RACSoft package are described below:

1. The bad pixel step removal replaces a number of pixels marked bad because of dust grains on the CCD or hot electron production. The bad pixels are replaced by an interpolated value based on the surrounding pixels.

2. The bias subtraction step subtracts the ADC digital offset from the image.

3. The image is converted to DN/s

4. The RAC and the OM uses an electronic shutter where the image data is fast clocked to a covered area of the CCD at the end of the exposure followed by a slower digitization of the image data. During the fast clocking each row experiences some additional light from other parts of the scene. The electronic shutter correction subtracts from row N the summed DN signal of row 0 to N-1 scaled by the time it takes to clock a row one step on the CCD.

5. The dark current correction step subtracts an estimated mean value of dark current based on the temperature of the CCD. This simple scheme (as compared to the SSI) is used because the RAC and OM has very low dark current production under Mars conditions.

6. The flatfield correction divide the image by the relevant flatfield for the given focus motor step (RAC).

7. The OM calibration is finished after the flat field correction since good absolute calibration data is not available for the OM.

8. The final step of the RAC calibration is to divide the image by the absolute calibration constant for the given focus motor step. The calibration constant is given by the ground absolute calibration at focus motor step 306 (near infinite focus) and a correction factor derived for the change in instantaneous field of view between focus step 306 and the active focus step.

Processing

Phoenix RAC RDRs are considered CODMAC Level 3 (Calibrated Data equivalent to NASA Level 1-A), Level 4 (Resampled Data equivalent to NASA Level 1-B), or Level 5 (Derived Data equivalent to NASA Level 1-C, 2 or 3). The RDRs are to be reconstructed from Level 2 edited data, and are to be assembled into complete images that may include radiometric and/or geometric correction.

Phoenix RAC instrument EDRs and RDRs will be generated by JPL's Multimission Instrument Processing Laboratory (MIPL) as part of the OPGS subsystem of the Phoenix GDS. RDRs will also be generated by the RAC science instrument team at the SOC facility at the University of Arizona, as well as at its home institution, Max Planck Institute for Solar System Research.

RDR data products will be generated by, but not limited to, MIPL using the Mars Suite of VICAR image processing software at JPL, and the RAC science instrument team using RACCAL software at the SOC facility at the University of Arizona and at the team's home institution at Max Planck Institute for Solar System Research. The RDRs produced will be 'processed' data. The input will be one or more Camera EDR or RDR data products and the output will be formatted according to the data product SIS [ALEXANDERETAL2008]. Additional meta-data may be added by the software to the PDS label.

Data

RDR products generated by MIPL will have a VICAR label wrapped by a PDS label, and their structure can include the optional EOL label after the binary data. RDR products not generated by MIPL may contain only a PDS label. Or, RDR products conforming to a standard other than PDS, such as JPEG compressed or certain Terrain products, are acceptable without a PDS header during mission operations, but may not be archivable.

The RDR data product is comprised of radiometrically decalibrated and/or camera model corrected and/or geometrically altered versions of the raw camera data, in both single and multi-frame (mosaic) form. Most RDR data products will have PDS labels, or if generated by MIPL (OPGS), dual PDS/VICAR labels. Non-labeled RDRs include JPEG compressed products and the Terrain products.

Software

The RACCal software pipeline was used to generate the RDR's included in this dataset.

Media/Format

The data set will initially be delivered and kept online. Upon Mission completion, the RAC Operations RDRs will be delivered to PDS on DVD.

Data Set Overview

This data set contains raw Robotic Arm Camera (RAC) operational data. If 12 to 8 bit scaling was commanded, these images HAVE NOT been transformed back to 12 bits. These images are only used to assess the morphology, topography, and geologic context of the lander site and should not be used for quantitative scientific purposes.

More information is found in ALEXANDERETAL2008, LEMMONETAL2007, and LEMMONETAL2008.

Processing

This documentation uses the Committee on Data Management and Computation (CODMAC) data level numbering system. The Phoenix Camera Payload EDRs referred to in this document are considered Level 2 or Edited Data (equivalent to NASA Level 0). The EDRs are to be reconstructed from Level 1 or Raw Data, which are the telemetry packets within the project specific Standard Formatted Data Unit (SFDU) record. They are to be assembled into complete images, but will not be radiometrically or geometrically corrected.

EDR data products will be generated by MIPL using the telemetry processing software mertelemproc at JPL. The EDRs produced will be raw uncalibrated data reconstructed from telemetry packet SFDUs and formatted according to this SIS. Meta-data acquired from the telemetry data headers and a meta-data database will be used to populate the PDS label. Missing packets will be identified and reported for retransmission to the ground as partial datasets. Prior to retransmission, the missing EDR data will be filled with zeros. The EDR data will be reprocessed only after all partial datasets are retransmitted and received on the ground. In these cases, the original EDR version will be overwritten.

Data

The data packaged in the camera data files will be decoded, decompressed camera image data in single frame form as an Experiment Data Record (EDR). The Full Frame form of a standard image data file has the maximum dimensions of 1024 lines by 1024 samples.

1. Full Frame EDR: Full Frame EDRs are stored as 16-bit signed integers. If 12-to-8 bit scaling is performed, then pixels are stored in 16-bit format and only the last 8 bits of the 16-bit integer are used.

2. Thumbnail EDR: Thumbnail EDRs are stored as 16-bit signed integers or 8-bit unsigned integers. If 12-to-8 bit scaling is performed, then pixels are stored in 16-bit format and only the last 8 bits of the 16- bit integer are used. The Thumbnail EDR is a sized down version of the original acquired image (i.e., camera returned pixel data), and size of the binary EDR image data is variable. However, the original acquired image is not always downlinked. The main purpose of a Thumbnail EDR is to provide an image summary using a very low data volume compared to the original image.

3. Sub-frame EDR: Sub-frame EDRs are a subset of rows and columns of the 1024 x 1024 full frame image. Sub-frame EDRs are stored as 16-bit signed integers. If 12-to-8 bit scaling is performed, then pixels are stored in 16-bit format and only the last 8 bits of the 16-bit integer are used.

4. Downsampled EDR: A downsampled EDR is a smaller version of the 1024 x 1024 full frame or subframed image using the following methods: 1) nearest neighbor pixel averaging, 2) pixel averaging with outlier rejection or 3) computing the median pixel value. Downsampled EDRs are stored as 16-bit signed integers. If 12-to-8 bit scaling is performed, then pixels are stored in 16-bit format and only the last 8 bits of the 16-bit integer are used.

5. Reference Pixels: The onboard CCD array has 16 pre-Reference dark pixels (12-bits) located at the beginning and 15 post-Reference dark pixels (12-bits) located at the end of each row. The values of these pixels indicate the bias level of the camera at the time of each observation. The Reference Pixel images were losslessly compressed for downlink. For complex design reasons, the last post-Reference pixel is a copy of the next-to-last post-Reference pixel. Following the last post-Reference dark pixel, at the very end of each row, is the camera hardware serial number (left-shifted by 4 bits if 12-bit data).

Software

Phoenix Camera Payload downlink processing software is focused on rapid reduction, calibration, and visualization of images in order to make discoveries, to accurately and expeditiously characterize the geologic environment around the lander, and to provide timely input for operational decisions concerning target selection. Key software tools have been developed at JPL by the MIPL, SSV, and APSS groups, at NASA Ames, and at the USGS/Flagstaff.

PDS-labeled images and tables can be viewed with the program NASAView, developed by the PDS and available for a variety of computer platforms from the PDS web site http://pdsproto.jpl.nasa.gov/Distribution/license.html. There is no charge for NASAView.

Media/ Format

The data set will initially be delivered and kept online. Upon mission completion, the RAC EDRs will be delivered to PDS on DVD.