Thumbnail image showing POES data over Brazil.

The NOAA series of polar-orbiting satellites carry onboard a Space Environment Monitor subsystem that measures Energetic Particles along the orbit path.

NOAA / POES Space Environment Monitor

NEWS: NOAA-18 was launched on May 20, 2005. SEM-2 data from NOAA-18 begin June 6th.
NOAA-18 data were reprocessed and posted online on July 17, 2006 (read more)
Revised NOAA-18 archive files see green section below.

NOAA's Polar Orbiting Environmental Satellites (POES) (formerly known as TIROS for Television and InfraRed Observation Satellite) carry a suite of instruments that detect and monitor the influx of energetic ions and electrons into the atmosphere and the particle radiation environment at the altitude of the satellite. Both phenomena vary as a result of solar and geomagnetic activity. Beginning with the NOAA-15 satellite, an upgraded version of the Space Environment Monitor (SEM-2) is being flown. A number of SEM-2 instruments have been procured and it is anticipated that the SEM-2 instruments will be included on the NOAA/POES satellites until superceded by the NPOESS satellite program sometime after 2010.

Because the SEM-2 instruments differ significantly from the earlier SEM-1, there has been a complete revision to the data processing and archiving process. A number of improvements have also been included. Among these are incorporating up-to-date satellite orbit information and magnetic field models in the calculation of various magnetic coordinates, and improved data quality control.

The Total Energy Detector (TED) is designed to measure the energy flux carried by auroral particles, both positively charged ions (assumed here to be protons) and electrons, into the polar atmosphere. The magnitude and spatial extent of this energy flux are good measures of both the level of auroral activity and the atmospheric response to that energy input.

The Medium Energy Proton and Electron Detector (MEPED) includes a set of solid-state energetic particle detectors that monitor the intensities of protons and electrons over a range extending from 30 keV to more than 200 MeV. Particles having those energies include the radiation belt (Van Allen belt) populations, the particles in energetic solar particle events (solar proton events), and the low energy portion of the galactic cosmic ray population. Enhanced fluxes of these particles entering the atmosphere can produce significant and widespread degradation in short-wave radio propagation; in extreme cases even radio blackouts. The energetic particles also contribute to astronaut radiation exposure, especially on high inclination orbit missions during energetic solar particle events.

This text was extracted from the SEM-2 documentation available below.

  • General time coverage by satellite:
    • TIROS-N 1978 - 1981
    • NOAA-6 1979 - 1986
    • NOAA-7 1981 - 1985
    • NOAA-8 1983 - 1985
    • NOAA-10 1986 - 1991
    • NOAA-12 1991 - 2002
    • NOAA-14 1994 - 2004
    • NOAA-15 1998 - present
    • NOAA-16 2001 - present
    • NOAA-17 2002 - present
    • NOAA-18 2005 - present
    • METOP-02 2006 - present (aka METOP-A)


  • A detailed archive catalog is updated automatically whenever data are received
  • All NOAA-18 data were reprocessed and the new files placed on line on 2006-01-06. The reason for the upgrade will be explained in the annual status report due out later this month.
  • Direct Access to POES SEM data (
    This link will take you to the access point for all POES SEM data. These data are updated daily. If you would rather optain these data on DVD-ROM at a nominal charge, contact The data available are the full-resolution archive files as described in the SEM-2 Archive File documentation below. A reduced resolution version of these data, with graphical browse capability is pending
  • Two data products improve access to POES SEM Data:
    On July 21st, 2004 16-second averages were generated from the two-second resolution archive for NOAA-15, NOAA-16, & NOAA-17. The averages are supplied in Common Data Format (CDF) and as standard text files. These two new products will make these data accessible to many users who previously couldn't use the data because they lacked the programming resources necessary to unpack the binary archive files. CDF is a self-documenting data format that is supported by a wide assortment of utilities and programming interfaces from the National Space Science Data Center. The text files can be opened with any text editor or word processor and have been specifically designed for easy import into commercial analysis software. The text files are described in a readme.txt file
    These products were produced by adapting software that was originally written by Sue Greer, Space Environement Center.

2008-04-22 MepOp Orbital Maneuvers

It has come to our attention that during instances when the MetOp satellite exercises orbital maneuvers the entire SEM-2 instrument is turned off.  Unfortunately the data processing software does not recognize when the SEM-2 data processing unit (DPU) has been turned off and so assumes that the data received from the TED and MEPED detectors, that had been turned off, are valid in spite of the fact those data are zero-fill during these periods.  The TED and MEPED instrument ON-OFF flags in the daily archive files are not properly set to OFF at these times.

Those periods of time during which the SEM-2 instrument on MetOp were turned off are:

April 19, 2007 between 0819:58 and 1616:14 UTC
April 24, 2007 between 0000:00 and 1359:27 UTC
July  12, 2007 between 0922:22 and 1538:22 UTC
Sept. 18, 2007 between 1454:10 and 2400:00 UTC
Sept. 19, 2007 between 0000:00 and 1402:58 UTC
Jan.  31, 2008 between 0921:30 and 1538:33 UTC
April  8, 2008 between 0732:23 and 2400:00 UTC
April  9, 2008 between 0000:00 and 0437:58 UTC

The TED and MEPED ON-OFF flags in the MetOp archive files for these days have been corrected and the corrected files are available.

2008-01-07 Revised NOAA-16 file for day 2007-07-09

It was discovered that orbital data contained in the NOAA-16 archive file for July 9, 2007 (day 190) was incorrect for times after 2035:11 UT. A revised NOAA-16 archive file for that day has been produced that eliminated records with incorrect orbital information.

2007-03-23 Revised NOAA-18 archive files

Revisions to NOAA-18 archive data files for July 23-24, 2005 and for the entire period July 11, 2006 through December 26, 2006 were necessary because incorrect calibration data for the TED instrument were used.  These revisions impacted only the TED auroral particle energy flux values and many of the data quality flags.  All of the MEPED data in the original archive data files were correct.

Users of TED data for these periods are advised to download the revised archive data files for NOAA-18.

2005-08-16 ERRATA: Software errors in unpackSem2.c since year 2000.

It has been brought to our attention by a user of POES SEM-2 data that the C language archive unpacking routine returns anomalous sensor values during periods where there are data missing as flagged by 999. We have examined that code and uncovered two significant errors in the C version of the code that have existed since 2000.

Both errors involve the way the C unpacker implements missing data flags. The first error centered around the fact that missing data flags associated with sensor data from the second half of the 32-second archive record were being improperly unpacked from the binary archive record. The consequences of that error were that TED and MEPED sensor values during periods when data were missing were often improperly flagged with valid data being set to -999. indicating missing data, while entries that should have been flagged as missing data were given count values of 19988488, the highest count value possible.

The second error also involved the implementation of missing data flags and impacted P8 and P9 omni-directional detector data throughout an entire 32-second archive record. The P8 and P9 data share the same data word in the TIROS data format and readouts alternate between the two. In the archive record the data listing for P8 alternates between valid data readouts and values set to 0 in the archive format while the P9 data alternates in the same fashion but with valid readouts when the P8 value is zero. The existing documentation explains this and a user is expected to extract only the appropriate entries when using P8 and P9 data. During instances when data were missing, the C unpacker assigned the missing data flag (-999.), in both the P8 and P9 data, to the entry appropriate to 'no data' while the entries appropriate to valid data were given count values of 19988488. This count value is unphysical for P8 and P9 data.

Both these errors would have impact upon any analysis that had not recognized these unphysical sensor count.

The FORTRAN version of the archive record unpacker did not have either of these problems.

David S Evans <>

Corrected sofware (unpackSem2_v2.c) is now available for distribution.

  • Static displays of NOAA data created for various projects:
    • NOAA-11 anomalies plotted on a background of NOAA-10 electron fluxes. (GIF)
    • Stack plots showing the NOAA-12 > .3 MeV electrons at L4.5 - L4.8 and GOES-8 > 2 MeV electrons at L6.6. These plots show the affect of smoothing on the NOAA-12 data, an algorithm for detecting NOAA-12 event start and peak times, and an exponential decay model for those events. (PDF, 12/23/98)