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GES DISC DAAC Data Guide:UARS PEM Level 3AT Data Set Document

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Summary:

The Particle Environment Monitor (PEM) is one of 10 instruments aboard the Upper Atmosphere Research satellite (UARS). It's purpose is to determine both the global input of charged-particle energy into the Earth's stratosphere, mesosphere, and thermosphere and the predicted atmospheric responses. Three separate boom-mounted sensors measure electrons, protons, and the strength of the Earth's magnetic field in the vicinity of the UARS spacecraft. PEM also includes a 16-element array of x-ray detectors to provide global images and energy spectra of brehmstrahlung x-rays produced by electrons precipitating into the upper atmosphere. Data collection began 01 October 1991 and continues to the present. This document describes the PEM level 3AT and 3TP data products available from the Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC).

NOTE: If you are looking for documentation and read software for PEM level 2 AXIS, HEPS, MEPS and VMAG data, please download the read_pem_l2.tgz (tar file).

Table of Contents:

1. Data Set Overview

Data Set Identification:

UARS PEM LEVEL 3AT DAILY TIME ORDERED DATA

UARS PEM LEVEL 3TP DAILY TIME ORDERED DATA

Data Set Introduction:

PEM is a multi-sensor instrument, which includes the High Energy Particle Spectrometer (HEPS), Medium Energy Particle Spectrometer (MEPS), Atmospheric X-ray Imaging Spectrometer (AXIS), and the Vector Magnetometer (VMAG). The PEM data are grouped into two data product classes: level 3AT and level 3TP. The 3AT data consist of time-ordered data records at 65.536 second intervals. The level 3AT measured parameters are electron, proton and x-ray (one for each of the 16 AXIS pixels) energy deposition rates. There are a total of 18 3AT products. The PEM level 3TP products contain electron and proton energy deposition rates by individual HEPS and MEPS sensors. These products are at a higher temporal resolution than corresponding electron and proton level 3AT data products (2.048 seconds for MEPS and 65.536 seconds for HEPS) which are only produced when there are simultaneous HEPS and MEPS measurements.

There are two PEM version 3 level 3A data products archived at the DAAC:

Level 3AT

PEM level 3AT data are daily time-ordered data of electron, proton and x-ray energy deposition rates, arranged at time intervals of 65.536 seconds, or about 495 km intervals along the line-of-sight (LOS) tangent track. The reference time at which level 3AT data are arranged is common across all UARS level 3AT files.

Level 3TP

PEM level 3TP data provide detailed energy deposition profiles of electrons and protons from the HEPS and MEPS instruments. The PEM 3TP data provide a higher temporal resolution than the corresponding level 3AT electron and proton data. The HEPS data are sampled at 65.536 second resolution, and the MEPS data are at 2.048 second resolution.

Objective:

The overall objective of the PEM level 3 data products is to provide comprehensive measurements of both local and global energy inputs into the Earth's atmosphere by charged particles. PEM provides information for pursuing six specific objectives:

  1. Determining the effects of energetic particles on stratospheric, mesospheric, and thermospheric chemistry,
  2. Determining ozone reduction induced by solar protons,
  3. Identifying sources of nitric oxide,
  4. Determining the effects of energetic particles on noctilucent cloud formation,
  5. Studying the physics of the inetraction of particle fluxes with the atmosphere, and
  6. Investigating anomalous ionization produced by energetic electrons.

Summary of Parameters:

The level 3AT data product contains the following parameters:

  • electron energy deposition
  • proton energy deposition
  • x-ray energy deposition

The PEM_L3TP_DAILY data product contains the following parameters:

  • electron energy deposition
  • proton energy deposition

Discussion:

Each PEM level 3AT data record contains time, latitude, longitude, solar zenith angle, local time, and an array of data, as well as an array of quality (standard deviation) values. Profiles of electron, proton and x-ray energy deposition rates cover the altitude range from 5 to 400 km. Coverage for AXIS ranges from -80 to +80 degrees. For HEPS and MEPS the coverage is from -59 to +59 degrees.

PEM created a special 3TP data product to provide higher temporal resolution for HEPS and MEPS electron and proton parameters.

HEPS data files contain the altitude where particles are assumed to be deposited, the latitude and longitude of the centered dipole model used, and for HEPS electron files, the distribution shape parameters (alpha parameters) in one data record. The rest of the data records in the file contain the derived energy deposition profiles and their standard deviations, along with time, latitude, longitude, and spectral fitting parameters.

MEPS data files contain time, latitude, and longitude markers, followed by the energy deposition profile measurements and corresponding standard deviations. Data are reported for each UARS altitude every 2.048 seconds.

Temporal and spatial coverage of the level 3TP data products are identical to those for level 3AT. Data file structures for the 3AT and 3TP file types are contained in the Standard Formatted Data Units (SFDU) documents listed in the Reference section below.

Related Data Sets:

All UARS level 3AL and 3AT files use the same formats to allow for intercomparisons of atmospheric profiles between the different instruments.

2. Investigators:

Principal Investigator:

Name:
J. David Winningham
Address:
Southwest Research Institute
Instrumentation and Space Research Division
P.O. Box 28510
6220 Culebra Road
San Antonio, Texas 78228-0510
Telephone Numbers:
Voice: +1-210-522-3075
FAX: +1-210-522-3075
Electronic Mail Address:
david@dews1.space.swri.edu

Title of Investigation:

Particle Environment Monitor

3. Theory of Measurements:

PEM determines the type, amount, energy, and distribution of charged particles injected into the Earth's thermosphere, mesosphere, and stratosphere. It utilizes three separate boom-mounted sensors to measure electrons with energies from 1 eV to 5 MeV, protons with energies from 1 eV to 150 MeV, and the strength of the Earth's magnetic field--all in the vicinity of the spacecraft. In addition to the in situ particle measurements, PEM includes a 16-element array of X-ray detectors to provide wide spatial coverage of the energy injected into the upper atmosphere by high-energy electrons. As these electrons are slowed in their passage through the atmosphere, X-rays are emitted and scattered in all directions. PEM provides X-ray images in the energy range from 3 to 100 keV, leading to the reconstruction of the global, three-dimensional energy input spectrum of electrons up to 1 MeV in energy.

4. Equipment:

Instrument Description:

Overview:

PEM is comprised of four types of instruments. These instruments are the Atmospheric X-ray Imaging Spectrometer (AXIS), the High Energy Particle Spectrometer (HEPS), the Medium Energy Particle Spectrometer (MEPS), and the Vector Magnetometer (VMAG). PEM is distributed over the UARS spacecraft with the HEPS and MEPS sensors located on the PEM zenith and nadir booms. They make in-situ measurements of precipitating electrons in the energy range of 1 eV to 5 MeV, and protons in the energy range of 1 eV to 150 MeV. VMAG is also located on the zenith boom and provides vector measurements of the local magnetic field using a 3-axis fluxgate magnetometer. AXIS measures Bremsstrahlung x-rays from the atmosphere in order to determine the remote electron energy deposition into the atmosphere. It provides global images and energy spectra of 1 to 100 keV brehmstrahlung x-rays produced by electrons precipitating into the upper atmosphere. AXIS is mounted on the nadir side of the spacecraft body at the opposite end from the multimission modular spacecraft (MMS) subsystem and performs its measurements over the global atmosphere.

  • AXIS

    AXIS measures the x-ray energy spectrum produced by energetic electrons incident upon the atmosphere. It includes 16 detector modules (pixels) that view the atmosphere from limb-to-limb. As the spacecraft orbits the earth, AXIS provides a "strip chart" image of the x-ray intensity on either side of the UARS ground track. AXIS measures x-rays in the energy range from 3 to 100 keV. Each pixel contains a solid-state silicon detector surrounded by tungsten and tantalum collimator shields. The pixels are passively cooled by a two-stage thermal radiator system to 160 degrees K to reduce detector leakage current and noise. AXIS looks forward of nadir (towards the +X spacecraft axis) by 22.5 degrees. The eight pixels of AXIS 1 (AXIS 2) view from near the spacecraft ground track to the limb on the -Y (+Y) side of the spacecraft. In the AXIS instrument, the x-ray spectrum of each detector is divided into 128 linear energy channels. They are compressed under microprocessor control for the down-link telemetry to 32 logarithmic channels per pixel every 8 seconds and also to four channels per pixel every 1 second. In addition, there are integral spectra for 10 pixels every 0.5 seconds.

  • HEPS

    HEPS observes the local precipitating (particles coming down the magnetic field line) and trapped (the mirroring particle distribution returning from the earth up the magnetic field line) electron and proton distributions at the spacecraft. Electrons are measured over 32 logarithmic energy steps from 30 keV to 5000 keV at angles of -15, +15, +45, and +90 degrees to the zenith. Positive angle is in the +X direction measured from the -Z axis of the spacecraft. These data are accumulated continuously and are read every 4 seconds. They are also observed from 30 keV to 1500 keV at angles of -165 and +165 degrees and are read-out every 16 seconds. Protons are detected over 32 logarithmic energy steps from 0.10 MeV to 150 MeV at angles of -15 and +15 degrees to zenith and in 24 energy channels from 0.50 MeV to 150 MeV at +45 and +90 degrees. They are read every 16 seconds. Additional integral counting rates are collected in each sensor telescope for both electrons and protons.

    The field of view for each of the eight particle telescopes is a cone 30 degrees wide. The multiple view directions resolve the angular distribution of electrons and protons to distinguish the precipitating particles from the trapped populations. Energy deposition in the atmosphere is produced by the precipitating electrons and protons. The geometric factor for the low-energy (0.10 to 0.50 MeV) proton sensors at -15 and +15 degrees is 0.07 cm2 sr. The geometric factor for the other HEPS 1 and HEPS 2 sensors is 0.54 cm2 sr. The geometric factor for both HEPS 3 telescopes is 1.53 cm2 sr. For angular coverage and redundancy there are three HEPS packages at two locations: on the PEM zenith boom are HEPS 1 with telescopes at +15 and +45 and HEPS 2 with telescopes at -15 and +90 degrees, while HEPS 3 is on the nadir boom with electron sensors at -165 and +165 degrees.

     

  • MEPS

    MEPS measures the local particle population in the range from 1 eV to 32000 eV. It generates a 31-point logarithmic energy spectra every two seconds. Telemetry restrictions force every other point of data from most of the ion sensors to be lost, resulting in 15-point energy spectra. Five MEPS analyzer heads are mounted on the zenith boom, each determining the electron and ion population simultaneously. Their positions are defined in spacecraft coordinates at +6.3, +21.3, -23.7, +36.3, and +66.3 degrees relative to the -Z spacecraft axis in the direction of +Y spacecraft axis (positive angle is in the +Y direction measured from the -Z axis). Three MEPS analyzers are mounted on the nadir boom and they only measure the electron population. Their positions are defined in spacecraft coordinates at +126.3, +156.3, and -158.7 degrees.

    Data from all MEPS sensors are not available at all times. When the spacecraft is flying with its velocity vector in the +X direction, data from electron sensors mounted at +21.3, -158.7, and the ion sensor mounted at +21.3 degrees are not available when the spacecraft is in the northern hemisphere. Data from electron and ion sensors mounted at -23.7 and +6.3 degrees are not available when the spacecraft is in the southern hemisphere. This reverses when the spacecraft is flying with its velocity vector in the -X direction. Here, data from electron and ion sensors mounted at -23.7 and +6.3 degrees are not available when the spacecraft is in the northern hemisphere, and data from electron sensors mounted at +21.3, -158.7, and ion sensor mounted at +21.3 degrees are not available when the spacecraft is in the southern hemisphere.

  • VMAG

    VMAG provides vector measurements of the local magnetic field using a 3-axis fluxgate magnetometer. The fluxgate sensor detects the ambient field in the following way. The sensor head consists of a pair of coils, a driver, and a sensor wrapped on a core of high-permeability material. An alternating current in the driver coil is used to force the core to saturation with alternating polarity. The sensor coil records the rate of change of flux that passes through the windings. In the absence of a background field, the polarity reversals of core magnetization occur equally spaced in time.

    VMAG serves two purposes, the first of which is to provide a reference for the plasma measurements which determine energy input from particle precipitation, and second to determine the energy deposited in the ionosphere by field aligned currents. The direction of particle precipitation relative to the local field determines the altitude in the atmosphere at which particles deposit their energy. Hence, knowledge of the local magnetic field is required to evaluate energy deposition due to precipitating particles from the energetic particle data acquired by PEM. In addition, deviations in the magnetic field result from current at or near the spacecraft, primarily flowing parallel to the magnetic field direction. VMAG data thus provides information on the current densities flowing into and out of the ionosphere and can be used to determine the energy deposited by the currents.

PEM has been collecting scientific data since 01 October 1991.

Collection Environment:

Satellite data are collected from a near-circular Earth orbit of about 585 km altitude and 57 degree inclination.

Platform:

Upper Atmosphere Research Satellite (UARS).

Platform Mission Objectives:

UARS was launched September 12, 1991 with the mission of investigating the chemical and dynamical processes of the Earth's upper atmosphere. See the UARS Project document for more information.

5. Data Acquisition Methods:

Data are telemetered from UARS through the Tracking and Data Relay Satellite System (TDRSS) to the Data Capture Facility (DCF) at NASA GSFC. From there the data are given an initial quality check, and are then forwarded to the UARS Central Data Handling Facility (CDHF). The instrument PI teams are connected to the CDHF through remote analysis computers (RACs), where they have developed software to convert the raw data to higher level processed data. The CDHF uses the production software to convert the level 0 (raw) data to level 1, 2, 3A and 3B data. The Goddard DAAC acquires the UARS data from the CDHF.

6. Observations:

Data Notes:

None at this time.

7. Data Description:

Spatial Characteristics:

Spatial Coverage:

Spacial coverage for AXIS ranges from -80 to +80 degrees. For HEPS and MEPS the coverage is from -59 to +59 degrees.

Spatial Coverage Map:

Data coverage for PEM looking southward on 5/22/1992.

Map showing UARS orbital tracks

Spatial Resolution:

Level 3AT: varies in latitude and longitude. Near the equator, latitude resolution is about 3 degrees.

Vertical resolution is 3 to 5 km.

Projection:

Not Applicable.

Grid Description:

All PEM level 3 data have been referenced to the UARS standard altitude grid. The index of the data array defines the altitude level in km:

  Z(i) = 5 * i,                 i <= 12
  Z(i) = 60 + (i - 12) * 3,     13 <= i <= 32
  Z(i) = 120 + (i - 32) * 5,    33 <= i <= 88

Temporal Characteristics:

Temporal Coverage:

Temporal coverage is from 01 October 1991 to the present. The GSFC DAAC has PEM level 3 data within three months of the current date.

Temporal Coverage Map:

In order to achieve data in the Level 3AT file, both the HEPS and MEPS data must be available and producing high quality data. There are times when one of these two instruments does not produce data correctly. There are two effects which usually cause this, (1) there was no sensor within the loss cone (pitch angle too big) and (2) there was charging contamination. The first condition can affect both particle detectors and usually occurs around the equator. The second occurs in MEPS data. Most of the data not reported in the Level 3AT file is due to this second effect. The individual instrument profiles are written in Level 3TP files.

Temporal Resolution:

The temporal resolution of PEM level 3A data granules is daily.

Data Characteristics:

Parameters:

There are 18 parameters for PEM level 3AT data products, and 4 parameters for PEM level 3TP data products. The parameters are classified according to PEM subtypes. The measured parameters are listed below with the original PEM subtype name, DAAC parameter name, and units:

 

Level 3AT
Subtype DAAC Parameter Name Units
EDEP3AT_ELEC ELECTRON ENERGY DEPOSITION erg/cm3/s
EDEP3AT_PROT PROTON ENERGY DEPOSITION erg/cm3/s
EDEP3AT_P01 X-RAY PIXEL 01 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P02 X-RAY PIXEL 02 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P03 X-RAY PIXEL 03 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P04 X-RAY PIXEL 04 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P05 X-RAY PIXEL 05 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P06 X-RAY PIXEL 06 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P07 X-RAY PIXEL 07 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P08 X-RAY PIXEL 08 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P09 X-RAY PIXEL 09 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P10 X-RAY PIXEL 10 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P11 X-RAY PIXEL 11 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P12 X-RAY PIXEL 12 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P13 X-RAY PIXEL 13 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P14 X-RAY PIXEL 14 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P15 X-RAY PIXEL 15 ENERGY DEPOSITION keV/g/s3/s
EDEP3AT_P16 X-RAY PIXEL 16 ENERGY DEPOSITION keV/g/s3/s

 

Level 3TP
Subtype DAAC Parameter Name Units
HEPS_ELEC_ED HEPS ELECTRON ENERGY DEPOSITION erg/cm3/s
HEPS_PROT_ED HEPS PROTON ENERGY DEPOSITION erg/cm3/s
MEPS_ELEC_ED MEPS ELECTRON ENERGY DEPOSITION erg/cm3/s
MEPS_PROT_ED MEPS PROTON ENERGY DEPOSITION erg/cm3/s

8. Data Organization:

Data Granularity:

The granularity of PEM level 3A data are defined such that there is one granule for each level and parameter subtype (see the Data Characteristics section above) per day, for a total of 22 granules per day. Each PEM level 3A granule is a multi-file granule consisting of two files:

  1. The binary data file (files ending with PROD, or *PROD extension) which contains the energy deposition profiles and corresponding standard deviation for each UARS altitude, along with satellite and instrument identifiers, time, latitude and longitude, local solar time, and solar zenith angle.
  2. An ASCII metadata file (files ending with META, or *META extension) associated with the data file containing items such as the begin date, end date, PI assigned quality flag and record length size of the data file.

     

  3. A binary parameter file (also *PROD extension). The subtype for these files is PARAM. A separate PEM 3TP parameter file is created for HEPS and MEPS electon data and HEPS and MEPS proton data. The 3TP files contain data profiles, identifiers for satellite and instrument, time, latitude and longitude. HEPS data also contains amplitude and fit parameters; MEPS data contains parameters associated with the MEPS Electron energy deposition results.
  4. An ASCII metadata file associated with the parameter file (also *META extension). The information is identical to the metadata file associated with the data file, except that the record length applies to the parameter file.

The naming convention for UARS granule file names distributed by the Goddard DAAC is as follows:

PEM_Llll_Sssss_Ddddd .Vvvvv_Ccc_xxxx,

where:

lll
is the UARS processing level (3AT or 3TP),
ssss
is the subtype or parameter),
dddd
is the UARS acquisition day (0001 = 12 September 1991),
vvvv
is the data version number,
cc
is the data version cycle number, and
xxxx
is the file extension (PROD for the binary files, or META for the ASCII metadata files)

For a full description of the naming convention see the "meta_desc.doc" file.

Average granule sizes range from 220 kB for level 3AT electron and proton files, and 900 kB for level 3AT x-ray files. Average granule sizes are 1.0 MB for level 3TP HEPS files, and 7.5 MB for level 3TP MEPS files. The *META files are small, about 700 bytes each.

Data Format:

The data are in a native UARS format (SFDU). The files were originally created on a VAX/VMS system at the UARS CDHF, and now exist as UNIX stream files at the Goddard DAAC. WINDII data file structures are presented in the Standard Formatted Data Units (SFDU) documents listed in the References section.

9. Data Manipulations:

Formulae:

Derivation Techniques and Algorithms:

The energy deposition and corresponding standard deviation are reported for each UARS altitude at the center of a UARS minute. Data are averaged for one UARS minute differently in different energy regions and then combined to form this file. The units for L3AT electron and proton reported value are erg/(cm**3-s). For L3AT Xray, the units for each reported value are keV/(g-s). UARS standard altitudes are placed in an array representing 88 altitudes. For indices(i) less than 12, the altitude is equal to 5*i. For indices between 13 and 32, the altitude equals 60 + (i - 12) * 3, and for indices between 33 and 88, the altitude equals 120 + (i - 32) * 5.

The Latitude and Longitude reported are in geodetic coordinates. They represent the position at DEPOSIT_ALTITUDE (=100 km) where the particles sensed at the spacecraft would precipitate in the atmosphere. Estimates of the location of precipitation are made using a centered dipole magnetic field model (see below).

Data Processing Sequence:

Processing Steps:

The PEM Electron Level 3AT file is generated by the production program PEMELECTRON_DEP. This program uses the PEM Level 2 data for input. The Level 2 read routines are accessed which return corrected data to the Level 3AT process in differential number intensity scientific units. Energy deposition calculations are made and the error terms are computed. Then the energy deposition values are mapped to the correct altitude based on the magnetic field line for that specific time and position of the spacecraft. These values are then written to the PEM electron Level 3AT file.

Processing Changes:

Reprocessing of the data occur about once a year.

Calculations:

Special Corrections/Adjustments:

Both HEPS and MEPS data need to be corrected for different effects. The HEPS proton data suffers from (a) solar photon contamination due to direct solar viewing, (b) an instrument dead time due to a finite amplifier response period, and (c) background contamination not screened by the anticoincidence detectors. The MEPS proton data suffers from contamination due to spacecraft charging. The negative spacecraft charge accelerates the thermal ion plasma and repels the low energy electron plasma. High velocity, high density thermal ions generate false proton signals within the MEPS detectors due to the reflection of ions from internal detector components. Normally, this would not be sensed, but because of the high intensity at high energies, the small probability for ion scatter becomes significant.

Level 2 read routines apply instrument corrections which may modify the quality fields stored in level 2 and these results are presented along with the data to level 3AT processing. It is suggested that these routines be used when accessing PEM HEPS and MEPS data. Corrections to both HEPS and MEPS data are non-trivial. Incorrect results will be obtained if level 2 data are accessed without using these level 2 read routines.

Confidence limits in the form of standard deviations for each data point are set using count rate statistics, the data compression error associated with each spectral value, and the range of expected values (based on similar previous satellite measurements). All input data are examined in the level 3AT processing.

Calculated Variables:

None.

10. Errors:

Sources of Error:

Confidence limits in the form of standard deviations for each data point are set using count rate statistics, the data compression error associated with each spectral value, and the range of expected values (based on similar previous satellite measurements). All input data are examined in the level 3AT processing.

Quality Assessment:

Data Validation by Source:

All data are checked by the PEM science team and assigned quality values. These values appear as the DATA_QUALITY_UARS fields in the ASCII metadata files. The format for DATA_QUALITY_UARS is a 3 character field of the form "p.q" where:

                VALUE       MEANING
         for p      0       Machine inspected
                    1       Qualitative evaluation
                    2       Intensive analysis
         for q      1       less than 50% good data
                    2       50% - 75% good data
                    3       76% - 98% good data
                    4       better than 98% good data

PEM does not use the optional DATA_QUALITY_PI field.

Measurement Error for Parameters:

At lower energies (in the thermosphere), the Level 3AT profile is quite consistent with the energy spectra. No abnormal anomalies have been seen. At high energies (>30 keV), the spectra shape is fit to a double power law. Forcing the high energy spectra to this shape can at times produce the effect of too much energy at the lower altitudes. A rudimentary check is made in order to determine reasonable deposition at low altitudes by examining the spectra. Grossly inconsistent estimates are zeroed at low altitudes, reflecting that there was no data measured in the highest HEPS energy steps. The method can project high energy intensities at lower altitudes which should have been measured by PEM if real.

Energy spectra which show a bump at high energies violate the condition required for the shape of a double power law. Since the double power law is a summation of two power laws, it requires that there be a region where each power law is dominant. Bumps in the high energy spectra can cause the power laws to dominate in the wrong region of the spectra. To avoid this, the high energy spectra is inverted and mirrored. This produces the proper shape for fitting, however, the price is that there is more dominance in the data which has a higher percentage error. In these cases, too much dominance may be generated by the small values at high energy and the result is that there is an incorrect fit of the data in the region of overlap between the two power law fits.

It is therefore cautioned that the energy deposition profile is a best estimate of energy input using this described procedure. For more detailed and accurate calculations, the user should use the energy spectra directly

Additional Quality Assessments:

During in flight operation all data will be tested for quality with an automatic data test program. PEM is an energy input instrument and the Level 3AT data products are altitude profiles of energy deposition rate determined for (a) incident electrons (HEPS and MEPS), (b) incident protons (HEPS and MEPS), and (c) incident electrons via the bremsstrahlung x-rays (AXIS). In the case of HEPS and MEPS data, the program will test the measured spectral form that is most directly related to energy deposition rate [erg/(cm2 s)] vs height. This spectrum will be an energy moment of the differential energy flux [erg/(cm^2 s eV)] as a function of energy. Upper and lower acceptance windows will be established, and each spectral value will be tested for fit within these limits. A flag based on location of data value within or outside the acceptance window bounds will be assigned. Confidence limits will be set using count rate statistics, the data compression error associated with each spectral value, and the range of expected values (based on similar previous satellite measurements). All data will be examined with this program.

Data Verification by Data Center:

Data files are checked to ensure that they are properly transferred and translated from their original VAX/VMS format at the UARS CDHF to the DAAC's UNIX format. No additional data checks are performed by the DAAC.

11. Notes:

Limitations of the Data:

The data files exist as UNIX stream files at the DAAC. Binary data are IEEE formatted. The binary data files should be read on 32 bit machines running UNIX operating systems. This is especially important for fields which are IEEE floating point values, such as the profile data and quality values. If you are going to use a non 32-bit and/or non-UNIX machine, then you will need to write your own conversion routines to read the data files.

File record length information is only listed in the ASCII metadata files (*META extension) which accompany the data and parameter files.

Known Problems with the Data:

See Special Corrections/Adjustments.

Usage Guidance:

Data included in this file is a combination of the energy deposited by both HEPS and MEPS every UARS minute. Its use is unrestricted, however there are two major assumptions which may effect the profile values which are generated. The first assumption is that the distribution is isotropic. Assuming isotropy means that the smallest pitch angle sensor was chosen from MEPS and HEPS independently. Data from HEPS and MEPS sensors are most likely taken at different pitch angles within the loss cone [cone is relative to the magnetic field which separates those particles lost to the atmosphere and those which remain in the magnetosphere. The instrument spectra from the minimum pitch angle sensor is taken to be representative of the electron distribution which is assumed to be isotropic. Therefore, no pitch angle dependence is accounted for in the energy deposition profiles.

 

Any other Relevant Information about the Study:

At lower energies (in the thermosphere), the Level 3AT profile is quite consistent with the energy spectra. No abnormal anomalies have been seen. At high energies (>30 keV), the spectra shape is fit to a double power law. Forcing the high energy spectra to this shape can at times produce the effect of too much energy at the lower altitudes. A rudimentary check is made in order to determine reasonable deposition at low altitudes by examining the spectra. Grossly inconsistent estimates are zeroed at low altitudes, reflecting that there was no data measured in the highest HEPS energy steps. The method can project high energy intensities at lower altitudes which should have been measured by PEM if real.

12. Application of the Data Set:

The study of important upper atmosphere processes such as energy balance, dynamics, and chemistry requires the global coverage that can only be achieved by remote sensing from space. The PEM sensors measure the energy radiated by the atmosphere, or the energy absorbed or scattered from sunlight passing through the atmosphere. Analysis of the results furnishes detailed information on chemical constituents, temperature, winds, and the effects of energy inputs from sunlight and the solar wind. These findings will help reveal the mechanisms that control the structure and variability of the upper atmosphere, improve the predictability of ozone depletion, and to define the role of the upper atmosphere in the Earth's climate systems.

13. Future Modifications and Plans:

Future reprocessing of the data are possible.

 

14. Read Software:

Software Description:

Simple read/dump programs are available for reading the PEM level 3A data files. The read programs are available in C and IDL languages.
 

Software Access:

To get the software use the links below:
 

15. Data Access:

Contacts Information:

Name:
Help Desk
Addresses:
NASA Goddard Space Flight Center
Code 610.2
Greenbelt, MD 20771
Telephone Numbers:
Phone: 1-301-614-5224
FAX: 1-301-614-5268
Electronic Mail Address:
gsfc-help-disc@lists.nasa.gov

 

Archive Identification:

The UARS PEM data are archived at the GES DISC under the UARS Project.

Procedures for Obtaining Data:

The PEM level 3A data files can be obtained from the GES DISC by several mechanisms. These include the following:

 

Data Archive Status/Plans:

The GES DISC currently supports PEM level 3A data products.

16. Output Products and Availability:

The PEM level 3A data are available. See the section above on Procedures for Obtaining Data for specific information. For more information on PEM, please refer to the PEM Home Page.

17. References:

Satellite/Instrument/Data Processing Documentation:

"The Upper Atmosphere Research Satellite (UARS) Mission", Reber, C. A., C. E. Trevathan, R. J. McNeal, and M. R. Luther, J. Geophys. Res. 98, D6, 10643-10647, 1993.

"The UARS Particle Environment Monitor", Winningham, J. D., et al, J. Geophys. Res. 98, D6, 10649-10666, 1993.

Journal Articles and Study Reports:

"Particle Environment Monitor Software Specifications, Data Descriptions, and Algorithms," Southwest Research Institute Document 7845-SDD, San Antonio, Texas. Referred to as the SDD document.

"The UARS Particle Environment Monitor," J. D. Winningham, J. R. Sharber, R. A. Frahm, J. L. Burch, N. Eaker, R. K. Black, V. A. Blevins, J. P. Andrews, J. Rudzki, M. J. Sablik, D. L. Chenette, D. W. Datlowe, E. E. Gaines, W. I. Imhof, R. W. Nightingale, J. B. Reagan, R. M. Robinson, T. L. Schumaker, E. G. Shelley, R. R. Vondrak, H. D. Voss, P. F. Bythrow, B. J. Anderson, T. A. Potemra, L. J. Zanetti, D. B. Holland, M. H. Rees, D. Lummerzheim, G. C. Reid, R. G. Roble, C. R. Clauer, and P. M. Banks, Journal of Geophysical Research, 98, 10649-10666, 1993.

Goddard DAAC IMS online documentation:

PEM WHOLE DATA SET SUPPLEMENT, NURSPE00.

PEM ELECTRON LEVEL 3AT DATA DESCRIPTION IN SFDU FORMAT, NURSPE43.

PEM PROTON LEVEL 3AT DATA DESCRIPTION IN SFDU FORMAT, NURSPE44.

PEM X-RAY LEVEL 3AT DATA DESCRIPTION IN SFDU FORMAT, NURSPE45.

PEM HEPS ELECTRON LEVEL 3TP DATA DESCRIPTION IN SFDU FORMAT, NURSPE46.

PEM HEPS ELECTRON LEVEL 3TP DATA DESCRIPTION IN SFDU FORMAT, NURSPE47.

PEM HEPS PROTON LEVEL 3TP DATA DESCRIPTION IN SFDU FORMAT, NURSPE48.

PEM MEPS PROTON LEVEL 3TP DATA DESCRIPTION IN SFDU FORMAT, NURSPE49.

UARS Granule Level File (*META) Description.

18. Glossary of Terms:

DATA PRODUCT
A collection of parameters packaged with associated ancillary and labeling data. Uniformly processed and formatted. Typically uniform temporal and spatial resolution. PEM level 3A data products include PEM_L3AL_DAILY and PEM_L3AT_DAILY. The PEM data product class is divided into data product subclasses according to measured parameters.

 

DATA SET
A logically meaningful grouping or collection of similar or related data. Data having mostly similar characteristics (source or class of source, processing level and algorithms, etc.) PEM is a subset of the UARS data set.

 

GRANULE
A Granule is the smallest aggregation of data which is independently managed.

 

PARAMETER
A measurable or derived variable represented by the data (e.g. air temperature, snow depth, relative humidity). At the Goddard DAAC, parameters are grouped into a Parameter General category, which is broken down into Parameter Specific.

19. List of Acronyms:

AXIS Atmospheric X-ray Imaging Spectrometer
CDHF Central Data Handling Facility
cm centimeter
DAAC Distributed Active Archive Center
DCF Data Capture Facility
EOS Earth Observing System
erg energy unit (1 erg = 10-4 Joule)
erg/cm-3/s energy deposition rate
FOV field of view
GSFC Goddard Space Flight Center
HEPS High-Energy Particle Spectrometer
IMS Information Management System
JPL Jet Propulsion Laboratory
KB kilobyte
keV kilo electron Volt
km kilometer
LOS line of sight
m meter
MEPS Medium-Energy Particle Spectrometer
PEM Particle Environment Monitor
NASA National Aeronautics and Space Administration
PI Principal Investigator
RAC Remote Analysis Computer
SFDU Standard Formatted Data Units
TDRSS Tracking and Data Relay Satellite System
UARS Upper Atmosphere Research Satellite
USO User Services Office
VMAG Vector Magnetometer

20. Document Information:

Document Revision Date:Fri May 10 11:54:11 EDT 2002

6 March 1998

Document Review Date:

Document ID:

Citation:

Document Curator:

Document URL:

http://disc.sci.gsfc.nasa.gov/DATASET_DOCS/uars_PEM_l3a_dataset.html

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