Abstract: The Particle Environment Monitor (PEM) on NASA's Upper Atmosphere Research Satellite (UARS) measures the type, amount, energy, and distribution of charged particles injected into the Earth's thermosphere, mesosphere, and stratosphere.
PEM consists of four instruments: the Atmospheric X-Ray Imaging ... Spectrometer (AXIS), the High Energy Particle Spectrometer (HEPS), the Medium Energy Spectrometer (MEPS), and the Vector Magnetometer (VMAG). AXIS produces global images of brehmstrahlung X-rays produced by energetic electrons incident upon the atmosphere in the 3 to 100 keV range. The instrument is made up of 16 silicon detector modules that view the Earth limb-to-limb. The HEPS and MEPS instruments provide in-situ measurements of precipitating electrons and protons. HEPS measures electrons in 32 logarithmic steps from 30 keV to 5000 keV, and protons are measured in 32 logarithmic steps from 0.10 MeV to 150 MeV. The MEPS instrument measures the local particle population in the energy range from 1 eV to 32000 eV, generating a 31 point logarithmic energy spectra every 2 seconds. MEPS consisted of five analyzer heads that determined the electron and ion population. Finally, the VMAG instrument observes the local magnetic field using a 3-axis fluxgate magnetometer.
The PEM instruments are distributed across the UARS spacecraft. Two HEPS (HEPS1 and HEPS2), one MEPS (ZMEPS), and the VMAG instrument are located on a zenith looking boom, called the Zenith Energetic Particle System (ZEPS). An Earth pointing boom, the Nadir Energetic Particle System (NEPS), contains one HEPS (HEPS3) and one MEPS (NMEPS). The AXIS instrument is mounted separately on the forward part of the UARS platform.
The PEM level 3AT data are time-ordered profiles spaced at intervals of 1 UARS minute (65.536 seconds), or approximately 495 km along the tangent track. The level 3AT format is common to all UARS instruments to allow for intercomparison. The PEM level 3AT data consist of 18 granules per day. A data granule is defined as one PEM subtype per day. The following subtypes are available:
1. EDEP3AT_ELEC - electron energy deposition 2. EDEP3AT_P01 - x-ray pixel 01 energy deposition 3. EDEP3AT_P02 - x-ray pixel 02 energy deposition 4. EDEP3AT_P03 - x-ray pixel 03 energy deposition 5. EDEP3AT_P04 - x-ray pixel 04 energy deposition 6. EDEP3AT_P05 - x-ray pixel 05 energy deposition 7. EDEP3AT_P06 - x-ray pixel 06 energy deposition 8. EDEP3AT_P07 - x-ray pixel 07 energy deposition 9. EDEP3AT_P08 - x-ray pixel 08 energy deposition 10. EDEP3AT_P09 - x-ray pixel 09 energy deposition 11. EDEP3AT_P10 - x-ray pixel 10 energy deposition 12. EDEP3AT_P11 - x-ray pixel 11 energy deposition 13. EDEP3AT_P12 - x-ray pixel 12 energy deposition 14. EDEP3AT_P13 - x-ray pixel 13 energy deposition 15. EDEP3AT_P14 - x-ray pixel 14 energy deposition 16. EDEP3AT_P15 - x-ray pixel 15 energy deposition 17. EDEP3AT_P16 - x-ray pixel 16 energy deposition 18. EDEP3AT_PROT - proton energy deposition
Units for energy deposition rate are in [erg/cm**3/sec]. The horizontal resolution of the level 3AT data product is about 495 km along the tangent track. The vertical resolution for the level 3AT PEM profiles is defined by the UARS altitude levels (in km) given by:
Z(i) = 5 * i, i <= 12 Z(i) = 60 + (i - 12) * 3, 13 <= i <= 32 Z(i) = 120 + (i - 32) * 10, 33 <= i <= 50
The electron and proton energy deposition level 3AT data are produced from the level 2 HEPS and MEPS data, and gridded to the 65.535 second level 3AT format. Data is only produced at times when there are simultaneous HEPS and MEPS measurements. For higher resolution there is the special PEM level 3TP data product.
The PEM level 3TP data are a special data product, and should not be confused with the level 3TP parameter files produced for the UARS MLS, HALOE, ISAMS, and WINDII. The PEM 3TP data provide a higher temporal resolution than the level 3AT data, and contain the HEPS and MEPS data in separate files. The HEPS data are at 65.536 second resolution, and the MEPS data are at 2.048 second resolution. The PEM level 3TP data consist of 4 granules per day:
1. HEPS_ELEC_ED - HEPS electron energy deposition 2. HEPS_PROT_ED - HEPS proton energy deposition 3. MEPS_ELEC_ED - MEPS electron energy deposition 4. MEPS_PROT_ED - MEPS proton energy deposition
Vertical resolution and data units are the same as for the level 3AT data.
Space Science Department
Southwest Research Institute
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Postal Code: 78228-0510
Chenette, D.L., D.W.Datlowe, W.L.Imhof, T.L.Schumaker, and J.D.Tobin, Global spectroscopy and imaging of atmospheric X-ray bremsstrahlung: Instrumentation and initial results from the PEM/AXIS instrument aboard the Upper Atmosphere Research Satellite, SPIE Vol. 1745, 1992.
... Reber, C. A., C. E. Trevathan, R. J. McNeal, and M. R. Luther, The Upper Atmosphere Research Satellite (UARS) Mission, J. Geophys. Res. 98, D6, 10643-10647, 1993.
Winningham, J. D., et al., The UARS Particle Environment Monitor, J. Geophys. Res. 98, D6, 10763-10775, 1993.
"Instrument Systems Description Document for the UARS Particle Environment Monitor (PEM)," Southwest Research Institute Document 7845-IS-1, San Antonio, Texas, (October 1990).