GOES Space Environment Monitor Format Description for 5- and 1-Minute Averaged Data July 8, 2005 It was brought to our attention that the ASCII files were in two different formats, i.e., exponents in some files were three digits and two digits in others. On this day all data were reprocessed with two digit exponents. FILE NAMING ----------------------------------------------------------- D075YYMM.TXT D -> Data version: 'G' GOES X-ray, Mag., Electrons & Uncorrected Proton Channels 'Z' GOES X-ray, Mag., Electrons & Corrected Proton Channels 'I' GOES X-ray, Mag., Electrons & Corrected Integral Protons 'H' GOES X-ray, Mag., Electrons & HEPAD 'A' GOES X-ray, Mag., Electrons & Uncorrected Alpha-Particles 07 -> GOES-7, etc. 5 -> 5-minute averages, 1 -> 1-minute averages YY -> year MM -> month Each file contains a descriptive header. SMS/GOES Satellite System The Synchronous Meteorological Satellites (SMS-1 and SMS-2) and the Geostationary Operational Environmental Satellites (GOES-1, GOES-2, etc.) all carry on board the Space Environment Monitor (SEM) instrument subsystem. The SEM has provided magnetometer, energetic particle, and soft X-ray data continuously since July 1974. Geosynchronous satellites have an unobstructed view of the sun for all but the few dozen hours per year when the Earth eclipses the sun. You can identify these intervals as gaps in the X-ray data near satellite local midnight in March-April, and September-October. These data are transmitted via direct telemetry to the Space Environment in Boulder, Colorado, and are available through the Solar-Terrestrial Physics Division of the National Geophysical Data Center, an organization in Boulder known internationally as World Data Center A for Solar-Terrestrial Physics. The volume of these data makes it impossible to issue a guarantee as to the quality of each and every data point. Users should be suspicious of ‘spikes’ in the data and attempt to correlate them with other sources before assuming that they represent the space environment. The time of these observations has not been corrected for the down-link and preprocessing delay which is within 1 - 5 seconds. Magnetometer Three orthogonal flux-gate magnetometer elements, (spinning twin fluxgate magnetometer prior to GOES-8) provide magnetic field measurements in three mutually perpendicular components: HP, HE and HN. HP is perpendicular to the satellite’s orbital plane. HE lies parallel to the satellite-Earth center line and points earthward. HN is perpendicular to both HP and HE, and points westward for GOES-4 and earlier satellites, and eastward for later spacecraft. X-ray Sensor (XRS) Ion chamber detectors provide whole-sun X-ray fluxes for the 0.5-to-3 (0.5-to-4 prior to GOES-8) and 1-to-8 Å wavelength bands. The X-ray sensors may experience significant bremsstrahlung contamination. This contamination is caused by energetic particles in the outer radiation belts and depends on satellite local time, time of year, and the local particle pitch-angle distribution. The X-ray sensors are also sensitive to background contamination due to energetic electrons that either deposit their energy directly in the telescope or strike the external structure and produce bremsstrahlung X-rays inside the ion chambers. Energetic Particle Sensor (EPS) Solid-state detectors with pulse-height discrimination measure proton, ?- particle, and electron fluxes. E1 and I1 channels are responding primarily to trapped outer-zone particles. The I2 channel may occasionally respond to trapped particles during magnetically disturbed conditions. The remaining proton integrals measure fluxes originating outside the magnetosphere -- from the Sun or the heart of the Galaxy. Users of GOES particle data should be aware that significant secondary responses may exist in the particle data, i.e. responses from other particles and energies and from directions outside the nominal detector entrance aperture. The integrated protons displayed in these plots have been partially corrected for these effects. Ion Data Quality Users of GOES particle data should be aware that significant secondary responses may exist in the particle data, i.e. responses from other particles and energies and from directions outside the nominal detector entrance aperture. A description of the algorithm that partially corrects for these effects is described below. Electron Data Quality The Electron detector responds significantly to protons above 32 MeV; therefore, electron data are contaminated when a proton event is in progress. Beginning with GOES-8 the electron data have had a preliminary correction applied, however, even these data are not to be considered research quality at this time. The GOES-5 electron channel is noisy from 1986 onwards and readings are a possible factor of 2 high. One component of the GOES-6 particle detector system has had radiation damage since 1986 that reduced its counting efficiency progressively. At present the E1 and P4 channels derived from this component record at only a few percent of their proper rates. In 1991 the telescope component of the GOES-7 energetic particle detector system experienced episodes of malfunction (noise). The first period began at 0330 UT, October 18, 1991 and extended to November 5, 1991. The detector was commanded off for 12 hours. At turn-on the detector appeared to have recovered, but failed again on November 11, with a rerecovery on November 12 after a second turn-off of three hours. The detector has since operated normally. The noise periods may be identified by unusually high rates being shown by the P1 channel and the derived > 1 MeV integral channel. Currently, the GOES-7 Energetic Particle Sensor is left turned off for 4 hours after eclipse to minimize bad data. More on GOES-8 through GOES-12 Electrons from Terry Onsager: 1. The GOES 11 satellite was in storage mode and spinning until June 2006. The electron fluxes vary with the spin of the spacecraft, and therefore the flux levels can easily be misinterpreted. It is safest not to use these data. 2. Three channel electron files contain > 0.6 MeV, > 2.0 MeV, and > 4.0 MeV data columns. There are questions with the geometric factor used for processing the 0.6 MeV electron channel (GOES-8 thru GOES-12). The relative variations of the 0.6 MeV electrons are useful for scientific studies, but spectral indices inferred from the 0.6 MeV and 4.0 MeV channels may not be accurate. 3. Five minute electron data are corrected for proton contamination, one minute values are not. The minimum value allowed in our processing is 1.33E-01. Our processing takes the accumulated electron counts in a short interval, converts to counts/second, and then subtracts off an estimated contamination from protons. When the electron count level is near the background level, the correction we do for proton contamination can take the count rate below zero. To avoid this we impose a floor on the count rate. I forget what this floor is, but when it's converted to flux, you get 1.33E-01. 4. You should not trust any data where the flux is below about 10 (cm2 s sr)^-1. Once you get near the background level of the instrument, the effect of the proton correction can be significant, even when the proton levels are near their background. Onsager, T. G., A. A. Chan, Y. Fei, S. R. Elkington, J. C. Green, and H. J. Singer, The radial gradient of relativistic electrons at geosynchronous orbit, J. Geophys. Res., 109, A05221, doi:10.1029/2003JA010368, 2004. Onsager, T. G., G. Rostoker, H.-J. Kim, G. D. Reeves, T. Obara, H. J. Singer, and C. Smithtro, Radiation belt electron flux dropouts: Local time, radial, and particle-energy dependence, J. Geophys. Res., 107(A11), 1382, doi:10.1029/2001JA000187, 2002. Onsager, T. G., R. Grubb, J. Kunches, L. Matheson, D. Speich, R. Zwickl, and H. Sauer, Operational uses of the GOES energetic particle detectors, SPIE Conference Proceedings, Vol. 2812, p. 281-290, GOES-8 and Beyond, Edward R. Washwell, ed., 1996. High Energy Proton and Alpha-Particle Detector (HEPAD) The HEPAD consists of a solid state / Cerenkov telescope and a photo-multiplier. An “alpha lamp” provides a reference pulse for calibrating the photo-multiplier in flight. The heading of each data files describes the data types and units contained therein, also, corrected and uncorrected data are so labeled. GOES Energetic Particle Correction Algorithm GOES Energetic Particle Correction Algorithm R. D. Zwickl NOAA Space Environment Laboratory In January 1990, an upgraded algorithm for calculating the energetic-particle differential and integral proton flux from measurements made by the energetic particle monitors aboard the GOES-6 and -7 satellites became operational in the Space Environment Services Center (SESC) of NOAA's Space Environment Laboratory (SEL). The following is a brief description of the rationale for the new algorithm and its basic features. Why Did We Need a New Algorithm? The energetic particle monitors are simple solid-state sensors, designed to handle large count rates without overwhelming the electronics. Since their launch these instruments have met their design goals and have never saturated, even during the largest events. However, because they were required to measure high rates, the detectors were built with passive shielding (no anti- coincidence); this has allowed particles to pass through the shielding from any direction and be counted as though they had entered through the front collimator. During solar energetic-particle events the low-energy passbands would detect particles at exactly the same time as the high-energy passbands did, even though it was impossible for the lower-energy particles to be present at such early times. During quiet times, cosmic rays and their secondary particles produce a very high background in the GOES sensors, in contrast to their effect on more advanced sensors that use active shielding (>100 times the "nominal" background). The initial algorithm, used until January 1990, did not take either of those effects into account. The Upgraded Algorithm The count rate as measured by any one of the seven energetic particle proton channels on GOES-6 or -7 (identical systems) can be given by Cm = Ct + S + BG, where Cm is the actual measured count rate, Ct is the true count rate, S is the count rate generated by particles entering through secondary energy passbands (i.e., those particles not passing through the collimator), and BG is the background count rate (produced primarily by cosmic rays). Simply stated, the new algorithm solves for Ct as follows: Ct = Cm - S - BG. The first step in the algorithm is to determine the background count rate for each of the seven channels. Since the background varies with time, a filter technique is used to find a new minimum value within the previous 10 days or use the previous value. This background value is then subtracted from Cm. Next, it is assumed that the energy spectrum of the energetic particles, from one energy channel to the next, can be represented by a simple power law in energy and that the secondary energy passbands that were determined during calibration are responsible for all of the secondary count rate. The resulting set of equations can then be solved, starting with the highest energy channel and working toward lower energies. All seven energy channels must contain data, or no values are calculated. Finally, each set of 5-minute-averaged values is calculated Independently of every other set of those values. This allows the corrected values to be calculated continuously in an operational environment.