APXS data sets

Data Set Overview

The Alpha-Particle X-Ray Spectrometer (APXS) is a contact instrument that uses X-ray spectroscopy to determine the elemental composition of soils and rocks. Atmosphere argon can also be measured by the APXS. The APXS is deployed on selected targets along the rover traverse to determine the elemental composition of samples. Materials processed by the Sample Acquisition - Sample Processing and Handling (SA/SPaH) system can also be delivered to the observation tray or to the martian surface for analysis by APXS. Elements heavier than Na can be detected by APXS. If present at sufficient levels, the abundances of these elements can also be determined. The instrument consists of a sensor head mounted on the rover's Robotic Arm (RA) component of the MSL SA-SPaH tools suite, and electronics mounted in the Rover Chassis. The APXS has access to an onboard calibration targets for post-landing calibration. The MSL APXS includes a Peltier cooler for the detector chip that can be activated to achieve better performance at daytime ambient temperatures. A total observation time of 2 to 3 hours is necessary for a full analysis; however, it is also possible to perform a quick analysis in about 15 minutes. For those familiar with the Mars Exploration rover (MER) APXS, these MSL observations times are shorter due to the different source-detector geometry. Other significant differences from MER include the cooler which expands daytime operations, and the need to transfer data to the rover computer prior to instrument power down (no memory backup). Similar to operations on MER, the rover may go to sleep to conserve energy once the APXS acquisition has started; however, the rover must be awake to stop the observation and retrieve the data.

Processing

APXS EDR data products are considered CODMAC Level 2 or Edited Data (equivalent to NASA level 0) products. The EDR data files are generated from Level 1 or Raw Data, which are the telemetry packets within the project specific Standard Formatted Data Unit (SFDU) record.

The APXS EDR data products will be generated by the MIPL (Multimission Image Processing Laboratory) at JPL under the Operations Product Generation System (OPGS). The EDR data products will be raw uncalibrated data reconstructed from telemetry data products in the format described by the APXS EDR SIS. Meta-data collected when the rover prepared the science data for downlink will be provided in PDS label. There will be multiple versions of an APXS EDR. If telemetry data is missing during the initial downlink from the rover memory, partial data sets will be created and the missing data will be filled with zeroes. The data will be reprocessed after all data are received and the original version will be overwritten. There can be up to 2 EDRs created, one with a status of partial and the other with a complete status in the filename.

Data

Each APXS EDR will consist 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 along with additional Rover FSW meta-data. The instrument holds data for the thirteen most recent measurements in memory. When a new measurement begins, the oldest one is discarded. Each spectrum has a unique identifier. There is also a data block containing instrument engineering data. There are 2 types of APXS EDRs: the APXS Science EDR and the APXS CWA (Current Working Area) EDR. The science EDR contains all 13 measurements and the engineering data. The CWA EDR only contains the most recent measurement.

Confidence Level Overview

The data presented in the APXS EDR is intended to be the least processed, most primitive data set released for APXS. Data presented here are an accurate representation of APXS data as received from the rover.

Review

The APXS EDR products are reviewed internally by the APXS team prior to release to the PDS. PDS also performs an external peer review of the APXS EDR.

Data Coverage and Quality

Data reported are the minimally processed data received from the orbiter during nominal APXS operations. All data received is reformatted into the EDR data. Data are by definition of good quality, as damaged telemetry packets are sequestered upon receipt from the spacecraft. We do not expect to receive many (if any) damaged data packets.

Limitations

The major limitation of this data set is that this is level 0, minimally processed data. The data are received from the spacecraft telemetry and ingested into a database. If gaps exist in the telemetry, data are lost.

Data Compression

No data compression is used.

Abstract

The MSL APXS RDR data set contains calibrated spectra and oxide weight percent data derived from observations of the APXS instrument aboard the Mars Science Laboratory rover. Two types of products are included: summed X-ray spectra in counts as a function of energy, and abundance data for a set of standard elements and oxides, derived from the summed spectra. Both product types are given as ASCII text files in comma-separated-value (CSV) format, suitable for reading with spreadsheet software.

Data Set Overview

The Alpha-Particle X-Ray Spectrometer (APXS) is a contact instrument that uses X-ray spectroscopy to determine the elemental composition of soils and rocks. Atmosphere argon can also be measured by the APXS. The APXS is deployed on selected targets along the rover traverse to determine the elemental composition of samples. Materials processed by the Sample Acquisition - Sample Processing and Handling (SA/SPaH) system can also be delivered to the observation tray or to the martian surface for analysis by APXS. Elements heavier than Na can be detected by APXS. If present at sufficient levels, the abundances of these elements can also be determined. There are two APXS RDR data products. The first product is the summed X-ray spectrum in counts as a function of energy, which is derived from the APXS EDR. The second product is the standard elemental oxide abundance, which is derived from the summed X-ray spectrum. Both products are stored as ASCII text in a Comma Separated Value (CSV) format. Each CSV file has an associated detached PDS label, also stored as ASCII text.

Processing

The APXS X-ray spectrum RDR products are considered CODMAC Level 4 or Resampled Data, equivalent to NASA level 1B. The spectra are generated from the APXS EDR products (CODMAC Level 2, NASA Level 0) archived in the PDS data set MSL-M-APXS-2-EDR-V1.0. The summed X-ray spectrum, product type RSP, is generated from the APXS EDR product by converting channel number to energy and summing together all buffers acquired at good temperatures. The RSP product consists of two fields, the first of which contains an energy value in eV and the second contains total counts for that energy channel. The count field value for first record is the counting time in seconds. The value for the last record is the overflow, that is, counts observed at that energy and higher. There is a header record at the start of the file that gives field headings for the two fields.

The APXS oxide abundance RDR products are considered CODMAC Level 5 or Derived Data, equivalent to NASA Level 2. The oxide abundance products, product type RWP, are generated from the X-ray spectra.

The oxide abundance product contains abundance data for a set of standard oxides and elements. There are three fields in the product: the oxide or element name, the weight percent, and the standard error of the weight percent value. The first record in the file is a header record that provides a description of the target sample.

Software

APXS RDR products are ASCII comma-delimited files that can be read using a text editor or with spreadsheet software such as Excel. No special software is required.

Confidence Level Overview

See CAMPBELLETAL2012 for a description of the calibration applied to the APXS data.

Review

The APXS RDR products are reviewed internally by the APXS team prior to release to the PDS. PDS also performs an external peer review of the APXS RDR.

Data Coverage and Quality

Nominally one APXS RDR spectrum is generated for each APXS EDR data product, and one APXS RDR oxide abundance product is generated for each RDR spectrum. Both the EDR and the RDR products may be revised during the course of the mission. Revisions are indicated in the product's PDS label by the keywords PRODUCT_VERSION_ID and PRODUCT_CREATION_TIME, and in the ERRATA.TXT file that accompanies the APXS archive.

Limitations

N/A

Data Compression

No data compression is used.