Overview: : The Electron Reflectometer high resolution (ERHR) data set is a time ordered series of electron measurements from the Lunar Prospector (LP) Mission. Each record consists of a time tag with 2 scalar data points representing measurements of the electron flux in 2 different energy channels, typically 140 and 340 eV, 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 accumulated over 1/2 spin (~2.5 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 ERHR data are provided as differential electron flux in units of particles per square cm per second per steradian per electron volt. ERHR measurements are recorded at 2 different energies, typically 140 and 340 eV. 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 1/2 spin), and the second dimension is energy (2 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. (The ER low resolution data set can be used for this purpose.) 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 2 energy bins (~140 & 340 eV) collected over a single spacecraft spin (~5 sec). The electron reflectometer 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 times and new set of energy bins are recorded in this second table. ER High Resolution Time Series Data: naming convention: EHyymmdd.TAB time: Time (UTC) in standard PDS format. high_res_spec: Array[2] giving omnidirectional electron flux in 2 energy bins. Format: time (A19), high_res_spec (1x,(2(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[2] giving 2 energy bins. Format: time (F15.0), UTC (1X,A20), energy_bin (F9.3,1x,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.

Review: : ER data quality has been reviewed at U.C. Berkeley by D. Mitchell, J. Halekas, M. Oieroset, T. Phan, S. Frey, and D. Curtis. Limitations: : The ERHR data are intended to be used in conjunction with magnetic field and spacecraft ephemeris data. 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. Data Quality: : The ERHR data are generally of very high quality. Three instrumental effects should be noted. (1) Sunlight directly enters the ER aperture twice per spacecraft spin. These photons scatter within the instrument and produce secondary electrons, which cause spurious counts. These counts have not been removed. (2) Electron fluxes are relatively high at low energies, and at times the instrument becomes saturated. A deadtime correction of the form 1/(1 - RT) is applied, where R is the measured count rate and T is the time needed to analyze a single electron. This correction is only reliable up to values of about 1.25, above which data are flagged. (3) Low energy electrons can be perturbed by the spacecraft floating potential relative to the plasma in which the spacecraft is immersed. In sunlight, the spacecraft floats a few volts positive, and in the Moon's shadow, it floats tens of volts negative. Electrons must cross this potential before they enter the ER electrostatic optics, thus all electron energies are shifted by this potential relative to their energies far from the spacecraft. No corrections are made for spacecraft potential effects. Data Coverage: : ERHR data are obtained continuously; however, telemetry gaps do occur. A table of gaps in the raw merged telemetry data (OUTAGES.TAB) is provided with this data set as a rough indication of the data coverage. Other gaps may exist due to data contamination or processing limitations.