MER1 (Opportunity) APXS Raw (EDR) Data Set Description Extracted from PDS3 Data Set Catalog File. Data Set Terse Description ========================== Mars Exploration Rover 1 Alpha Particle X-ray Spectrometer raw science and instrument data. Data Set Description ==================== Data Set Overview ================= This APXS (Rieder et al., 2003) data set contains data useful for determining the major and minor elemental composition of Martian soils, rocks, and other geological materials that the rover encountered. The raw (EDR) data products are raw uncalibrated data reconstructed from telemetry data products and formatted according to the APXS EDR Software Interface Specification. Metadata acquired from the telemetry data headers were used to populate the PDS label. Processing ========== The APXS raw data products were generated by the MIPL (Multimission Image Processing Laboratory) at JPL under the Operations Product Generation Subsystem using the telemetry processing software, mertelemproc. If telemetry packets were missing during the initial downlink from the rover memory, partial data products were created and the missing data were filled with (zeroes). The data were reprocessed after all data were received and the original version was overwritten. The APXS memory is maintained by a battery, and in theory, retransmits from the APXS memory could be commanded. In this instance, a new data product was created, because there might be subtle and potentially useful changes in the data when a retransmit from the APXS memory was commanded. Data ==== Each APXS raw product consists of two files. The first file is an ASCII formatted detached PDS label. The second file is a binary data file. The APXS EDR data file is a copy of what was in the APXS memory buffer. That is, the EDR consists of unprocessed experiment data stored in binary format. The APXS EDR contains energy spectra in units of counts and temperature values. Temperatures are derived from the two temperature sensors. There are two types of APXS spectra in each measurement: one x- ray, and two alpha spectra. The energy scale is divided into discrete channels with 256 channels for the alpha spectra and 512 channels for the x-ray spectra. The instrument holds data for the twelve most recent measurements in memory. When a new measurement begins, the oldest one is discarded. Each spectrum has a unique identifier. There are also 2 Kbytes at the end of the APXS EDR data file that are transferred from the instrument's internal RAM. This 2 Kbyte section of RAM is used for instrument engineering data. Starting around sol 3200, the rover science and engineering team implemented a new procedure to read out the APXS data twice for each integration. The procedure addresses the rare condition in which the rover wakes up and cannot access its flash memory. When flash memory is not available to the rover, it stores collected data in volatile memory, which is not saved when the rover shuts down. If this flash issue happens when the rover wakes up to read out the APXS data from the instrument, the APXS data are saved in volatile memory instead of flash, and are therefore lost when the rover next shuts down. The first time this condition impacted the Opportunity APXS experiment was on sol 3082, when the data for an atmospheric integration were lost. This procedure became standard practice when the rover flash memory failed and the rover operated on volatile memory only. The new procedure for an APXS integration that ends in the evening or at night is to switch on the APXS instrument right before the next downlink and read out the data from the instrument again, which are stored in the non- volatile APXS instrument memory. The second readout should be downlinked even if the rover is using its volatile memory. This means that there are two duplicate raw (EDR) products for all APXS integrations acquired after sol 3200 if there was no flash issue with the first readout. They will have different product IDs and therefore different file names. The duplicate raw product is indicated in the index table by a value of '2' in the column named DUPLICATE, the last column in the table. The raw product with the original readout from the instrument is indicated by a value of '1' in the DUPLICATE column. The APXS team, however, produces only one higher-level product if there are duplicate raw product and generally uses data from the first readout. Reference ========= Rieder, R., R. Gellert, J. Bruckner, G. Klingelhofer, G. Dreibus, A. Yen, and S. W. Squyres (2003) The New Athena Alpha Particle X-Ray Spectrometer (APXS) for the Mars Exploration Rovers, J. Geophys. Res., 108(E12), 8066, doi:10.1029/2003JE002150.