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Link to PEM Data
Products
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. Currently, PEM level 3AT and
3TP data products are available from the Goddard
Space Flight Center (GSFC) Distributed Active Archive Center
(DAAC).
UARS PEM LEVEL 3AT DAILY TIME ORDERED DATA
UARS PEM LEVEL 3TP DAILY TIME ORDERED DATA
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.
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:
- Determining the effects of energetic particles on stratospheric,
mesospheric, and thermospheric chemistry,
- Determining ozone reduction induced by solar protons,
- Identifying sources of nitric oxide,
- Determining the effects of energetic particles on noctilucent
cloud formation,
- Studying the physics of the inetraction of particle fluxes with
the atmosphere, and
- Investigating anomalous ionization produced by energetic
electrons.
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
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.
All UARS level 3AL and 3AT files use the same formats to allow for
intercomparisons of atmospheric profiles between the different
instruments.
- 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
Particle Environment Monitor
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.
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.
Satellite data are collected from a near-circular Earth orbit of
about 585 km altitude and 57 degree inclination.
Upper
Atmosphere Research Satellite (UARS).
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.
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.
None at this time.
Spacial coverage for AXIS ranges from -80 to +80 degrees. For HEPS
and MEPS the coverage is from -59 to +59 degrees.
Data coverage for PEM looking southward on 5/22/1992.
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.
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 coverage is from 01 October 1991 to the present. The GSFC
DAAC has PEM level 3 data within three months of the current
date.
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.
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 |
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:
- 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.
-
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.
- 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.
- 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.
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.
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).
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.
Reprocessing of the data occur about once a year.
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.
None.
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.
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.
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
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 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.
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.
See Special Corrections/Adjustments.
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.
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.
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.
Future reprocessing of the data are possible.
Simple read/dump programs are available for reading the PEM level 3A
data files. The read programs are available in both Fortran and C
languages. These programs simply print the file contents to the
screen.
The *META and *PROD files (see the Data
Granularity section) must be kept in the same directory, because
the programs require the *META file as the input parameter in order to
read the *PROD file. The *META file is necessary because it contains
file record length information, which is not in the *PROD files.
If you are using the Fortran READ programs you may need to change
the OPEN statement. Some machines read 4 byte words, while other
machines read 1 byte. If the program isn't working correctly, you
should try changing RECL=RECSIZ/4 to RECL=RECSIZ.
Contact science@eosdata.gsfc.nasa.gov for problems
with the read/dump software.
To compile the programs, just type:
f77 FILE_NAME.F -o FILE_NAME (Fortran programs)
or
cc file_name.c -o file_name (C programs)
Below are examples showing how to run the programs:
$ READUMP_L3AT_DATA (Fortran program)
PLEASE ENTER META DATA FILE NAME BELOW:
PEM_L3AT_SH2O_D0001.V0003_C01_META
or
$ readump_l3at_data PEM_L3AT_SH2O_D0001.V0003_C01_META (C program)
- 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:
- daacuso@daac.gsfc.nasa.gov
The UARS PEM data are archived at the GSFC DAAC, and can be
identified by the attributes listed below.
Data Set = UARS
Data Product = PEM L3AT DAILY LAT ORDERED
PEM L3TP DAILY TIME ORDERED
The PEM level 3A data files can be obtained from the Goddard DAAC by
several mechanisms. These include the following:
-
The DAAC Web-Based Archive
Interface provides a means for searching and ordering
data. To search the data holdings and place an order, go to the
DAAC Home Page located at "/index.shtml", and click on the "Search
and Order" icon. Next, pick the "Data Set" link, and from there
choose "UARS".
-
Anonymous
FTP. The most recent month of PEM data (about 2 months
from current) can be downloaded from the DAAC anonymous FTP server
located at daac.gsfc.nasa.gov, in directory
http://disc.sci.gsfc.nasa.gov/data/uars/pem. This area can also be
accessed through the World Wide Web at
ftp://daac.gsfc.nasa.gov/data/uars/pem. For convenience, the data
files are arranged in directories by instrument, level, and subtype
(e.g. http://disc.sci.gsfc.nasa.gov/data/uars/pem/3at/edep3at_p15/).
-
Earth
Observing System Data Gateway (EDG). You can place
orders for the UARS data through the Earth Observing System (EOS)
Data Gateway. From here you can also order data products from other
data centers. The web address for the EDG is
"http://eos.gsfc.nasa.gov/imswelcome/".
- DAAC Help
Desk. Data can also be obtained by contacting the GSFC
DAAC Help Desk listed above.
Data can be ordered electronically (FTP).
The DAAC currently supports PEM level 3AL and 3AT data products.
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.
"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.
"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.
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.
- 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.
| 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 |
-
- 6 March 1998
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http://disc.sci.gsfc.nasa.gov/DATASET_DOCS/uars_PEM_l3a_dataset.html
 UARS Project
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Atmos Composition
