LP ELECTRON REFLECTOMETER OMNI DIR. ELECTRON FLUX 80SEC V1.0 (PDS)

Description

This description was generated automatically using input from the Planetary Data System. Overview: ======== The Electron Reflectometer low resolution (ERLR) data set is a time ordered series of electron measurements from the Lunar Prospector (LP) Mission. Each record consists of a time tag with 15 scalar data points representing measurements of the electron flux in 15 different energy channels, usually ranging from 40 eV to 20 keV, with an energy resolution of 25%. Each data point is a measure of the electron flux (cm-2 sec-1 ster-1 eV-1) averaged over 4-pi steradians. These data are averaged over 16 spins (~80 sec) and are measured continuously. These data are intended to be used in conjunction with LP Magnetometer (MAG) data records, which provide the magnetic field vector as a function of time. Electrons travel along the magnetic field lines in tight helices (few km radius) at high speed (roughly one Mars diameter per second). Thus the electron data contain information about the plasma environment as well as the large-scale configuration of the magnetic field, which is sampled locally by the MAG. Parameters: ========== The ERLR data are provided as differential electron flux in units of particles per square cm per second per steradian per electron volt. ERLR measurements are recorded at 15 different energies, usually ranging from 40 eV to 20 keV. The energy sweep was changed several times during the mission for both instrumental and scientific reasons. A record of these sweep changes is provided in a detached table, with energies given in electron volts. Processing: ========== Processing is carried out at the Space Sciences Laboratory (SSL) of the University of California, Berkeley (UCB), to convert the raw data to measurements of the omnidirectional electron flux (cm-2 s-1 ster-1 eV-1) as a function of time. Because of the instrument's high dynamic range (six decades), the onboard digital processing unit (DPU) compresses the raw counts in a logarithmic scale. The first step is to decompress the raw counts and construct a two-dimensional data array, where the first dimension is time (1 element every 16 spins), and the second dimension is energy (15 elements). Raw count rate (R) is obtained by dividing the raw counts by the integration time, which is a function of energy. In general terms, the integration time is longer at higher energies in order to improve counting statistics. The data are next corrected for deadtime. During the time it takes the instrument to process a single electron (known as the ''deadtime'', which is about 0.3 microsec for the ER), it ignores any other electrons. The raw count rate is multiplied by the factor 1/(1 - RT), where T is the deadtime, to obtain the corrected count rate. Data values are masked when the deadtime correction factor exceeds 1.25. Note that a background count rate due to cosmic rays and noise in the electronics (about 10 counts/sec) has not been subtracted. In most cases, measurements in the highest energy channel (20 keV) are dominated by background, which allows this channel to be used as a baseline for estimating the background level in lower energy channels. Finally, one divides by the geometric factor (0.02 cm2 ster) and the center energy (eV) to obtain the differential particle flux (cm-2 s-1 ster-1 eV-1). Media/Format: ============ Data are archived on CDROMs in level 1 compliance with the ISO 9660 standard. Most CDROMs contain 23 days of data. The data set consists of two types of ASCII tables: data and energy bins. The data are provided as ASCII ''tables'' of 1 day duration. Fluxes are provided for 15 energy bins (~40-20000 eV) collected over sixteen spacecraft spins (~80 sec). The ER section of the instrument samples 4 pi steradians twice each spin period. The second table is a collection of the energy bin values. The instrument can be commanded to acquire data in a number of different sets of energy bins. In practice, the energy bins are not changed frequently. The time, and new set of energy bins are recorded in this second table. ER Low Resolution Time Series Data: naming convention: ELyymmdd.TAB time: Time (UTC) in standard PDS format. low_res_spec: Array[15] giving omnidirectional electron flux in 15 energy bins. Format: time (A19), low_res_spec (1X,15(1X,E9.3)) Energy Bin Change Table (E_BINS.TAB): time: Time (seconds since Jan 1, 1970) of the change to a new instrument configuration. UTC: Time (in PDS standard time format) of the change to a new instrument configuration. energy_bin: Array[15] giving 15 energy bins. Format: time (F15.0), UTC (1X,A20), energy_bin 15(1X,F9.3) Ancillary Data: ============== There are several ancillary data files provided with this archive. These include: Spacecraft Attitude data LP-L-ENG-6-ATTITUDE-V1.0 Spacecraft Ephemeris data LP-L-6-EPHEMERIS-V1.0 Spacecraft Position data LP-L-6-TRAJECTORY-V1.0 Spacecraft Command logs LP-L-ENG-6-COMMAND-V1.0 These data sets provide additional information about the state of the spacecraft and the instrument during data acquisition that may aid in the scientific analysis of this data set. Coordinate System(s): ==================== Software: ======== There are no software provided with this data archive.