LRO LAMP Reduced Data Record (RDR)

RDR – Reduced Data Record

Instrument: Lyman-Alpha Mapping Project

PDS Data Set ID: LRO-L-LAMP-3-RDR-V1.0DOI: 10.17189/1520338

For more information about LAMP RDR products, see the RDR Product SIS.

For more details on the structure and contents of the LAMP RDR Archive, see the RDR Archive SIS.

The Lyman-Alpha Mapping Project (LAMP) Reduced Data Record (RDR) data products consist of a calibrated and processed Experiment Data Record (EDR) data product in a single FITS formatted file on a one file per orbit basis containing ten types of data: calibrated spectral image (aperture door open), calibrated spectral image (aperture door closed), acquisition list, calibrated pixel list mode date, ancillary data, calibrated histogram mode data, calibrated calculated count rate, LTS data, housekeeping data, and a wavelength lookup image.

RDR Product Contents

Calibrated spectral image (aperture door open): This is a reconstructed histogram generated from the pixel list data in the EDR data product but with instrumental calibrations applied. When housekeeping data are available, only the pixel list data acquired when the aperture door was open are included in this dataset. Otherwise, all pixel list data are included in this histogram. This summary image is used as a “quick-look” check on data quality. [Extension 0 = primary FITS header and data unit (HDU)]

  1. Calibrated spectral image (aperture door closed): This is similar to the first dataset, but the reconstructed histogram here is generated from pixel list data acquired when the aperture door was closed. If housekeeping data are available, this dataset will be empty. This summary image is used as a “quick-look” check on data quality. [Extension 1]

  2. Acquisition list: This dataset contains a list of the generated frame acquisitions as determined from the housekeeping data file. These data are simply copied as is from the EDR data product. The frame acquisition times and instrument state data contained in this list are used to cross-reference with the pixel list mode in Extension 3 for purposes of selecting data and checking timing consistency. [Extension 2]

  3. Calibrated pixel list mode data: This dataset contains a calibrated version of the complete pixel list science dataset from the EDR data product, plus propagated estimated errors introduced by the separate calibration steps, plus ancillary spatial location and pointing information that is needed on a per-photon basis. These are the primary science data for use in making maps and other pixel list derived science products. [Extension 3]

  4. Ancillary data: This dataset contains ancillary spatial location and pointing information that varies smoothly and slowly over the LRO orbit. Also included in this extension are other slowly varying instrument-related quantities such as the detector locations of the STIM pixels, a measure of the background dark signal, and data quality flags. Entries in this table are typically separated by one-minute intervals instead of on a per-photon basis in order to reduce data volume and computation time. [Extension 4]

  5. Calibrated histogram mode data: This dataset contains a calibrated version of the complete histogram science dataset from the EDR data product, plus propagated estimated errors introduced by the separate calibration steps. If there are N histogram mode spectral images in the input EDR data product, this extension will consist of a stacked image cube containing 2N total images (i.e., N data + error image pairs). If N is greater than 1, then the Acquisition list (Extension 2) will be used to time-order the data + error image pairs within the image cube, from earliest to latest. If the input EDR data product contains only pixel list data, which will normally be true, then this extension will be empty. [Extension 5]

  6. Calibrated calculated count rate: This dataset contains a high-resolution sequence of UV photon count rates computed from the calibrated pixel list data for each acquisition (nominally the whole orbit). The resolution of this count rate sequence depends on the commanded “hack time” interval. If no pixel list science data are available, e.g., if data are acquired only in histogram mode, then this dataset will be empty. This sequence will be used to assess the variation in bulk far-UV signal throughout the orbit, and may be especially useful when trending data obtained near the terminator or during exceptional events (e.g., solar flares). [Extension 4]

  7. LTS data: LAMP housekeeping data contain up to 10 values per second of gain and offset corrected measurement values from each of the two LAMP Lunar Terminator Sensors (LTS). This dataset provides the full 10-Hz LTS dataset. These data are simply copied as is from the EDR data product. These coincident LTS data will be used with the count rate sequence in Extension 6 to confirm that LAMP is viewing the appropriate day/night/shadow scenes. (Raw 14-bit LTS data sampled at the 1-Hz HK rate is included together with this 10-Hz gain and offset corrected LTS dataset in the housekeeping data Extension 8.) [Extension 7]

  8. Housekeeping data: This dataset contains the complete housekeeping dataset, both in raw format and, where applicable, in calibrated engineering units. These data are simply copied as is from the EDR data product. HK data are included here to assist with joint instrument and data quality trending analyses (foreseen and unforeseen). [Extension 8]

  9. Wavelength lookup image: This dataset contains a 1024 x 32 image whose floating-point pixel values are the wavelengths corresponding to the pixel locations on the detector. This wavelength calibration image is provided to be used with Extensions 0 and 1 for quick-look checks, but not for scientific analysis. Its file-averaged wavelength solution makes it generally unsuitable to be used with pixel list data. [Extension 9]

RDR Product Processing

In order to create the RDR product, two primary types of conversions are applied to the EDR data product: (1) instrumental corrections and calibrations, and (2) spatial location determination. In general, six different types of instrumental corrections and calibrations are performed:

  1. Deadtime correction: This accounts for the fact that the LAMP microchannel plate (MCP) detector is insensitive to the detection of new UV photons for a short period of time following a previous detection, and this deadtime effect typically increases with increasing flux.

  2. Dark count correction/characterization: This is done because the LAMP MCP detector will generate some very low level of events in the complete absence of UV illumination. Thus, these spurious detections need to be subtracted out in order to get a better estimate of the true flux of UV photons.

  3. Flatfield normalization: This is performed to account for variations in sensitivity across the LAMP MCP detector in the spatial dimension.

  4. Effective area normalization: This is performed to account for the fact that the effective area (i.e., the sensitivity) of the LAMP instrument aperture is wavelength dependent.

  5. Wavelength lookup image: This is created in order to specify the UV wavelength associated with each pixel of the detector.

  6. Stray light correction: This correction accounts for instrument scattered light outside of the viewing science contaminating the observation. An estimated signal level is subtracted, e.g., based on proximity to the terminator and/or known sunlit peaks when viewing the night side. This estimation will be developed either from a detailed instrument simulator or analytical assessment of the collection of contaminated datasets (if any). The reliability of the scattered light estimation method requires in flight commissioning and/or science data and further demonstration; this effect might be treated by setting larger estimated (systematic) errors instead if this method proves unreliable. This effect may be left untreated if the scattered light is shown to be negligible.

The deadtime, flatfield, and effective area corrections and calibrations results in a weighting factor to be applied to each detected UV photon. The end result is that each detected photon represents a number of “actual” photons that is slightly different than unity.

Normally, each LAMP RDR data product contains calibrated observational data taken during a single LRO orbit. Thus, using a value of 113 minutes for the orbital period of LRO, LAMP generates approximately 13 data product files per day.

LAMP RDR products have the following file names:

LAMP_SCI_nnnnnnnnnn_vv.FIT (with detached PDS label)

where:

nnnnnnnnnn = 10-digit time stamp value, namely the Spacecraft UT (SCUT) of the start of the file

vv = 2-digit version number to facility unique identification of (possibly reprocessed) EDR data files

In ODE, RDR products have the following product IDs:

LAMP_SCI_NNNNNNNNNN_VV.FIT