00readme.txt -------- NSSDC contact: D. Bilitza ------------ Nov 20, 2001 This is the readme file for the Student Nitric Oxide Explorer (SNOE) daily NO density UVS data. These are Version 2 data (see version2.txt) Subdirectories: /1min_cdaweb These are 1-min averages of NO density in the altitude range 100 to 150 km in CDF format. The data can be viewed on CDAWeb. /NO_orb_avg_geo_ascii These are orbit averages of NO density using 5 degrees bins in geographic latitude, 3.3 km in altitude, and 24 degrees in geographic longitude (Level 3 data). The data layout is illustrated in file_layout_l3.jpeg. The data are provides as a 38x20 array. The 18th to 20th row provide the latitude, longitude (degrees) and UTC time (seconds), respectively. The last column lists first the altitudes (km) and then the Day-of-Mission (#18), Day-of- year (#19), and year (#20). The data are binned in geographic coordinates. The filenames are "yyyyddd_nn_snoe_uvs_orb_avg_geo_v02.asc" where yyyy is the year, ddd is the day of year, and nn is the orbit number of the day running from 00 to 14. NOTE: The first and last two data values (latitudes: -90,-85, 85, 90) contain fill values (0); Rows 18, 19, and 20 do not include carriage returns and therefore are combined here in a single row. /NO_orb_avg_mag_ascii Same as /NO_orb_avg_geo_ascii but now binned in geomagnetic coordinates. The filenames are "yyyyddd_nn_snoe_uvs_orb_avg_mag_v02.asc". /NO_daily_geo_ascii These are daily averages of NO density using 5 degrees bins in latitude and 3.3 km in altitude (Level 4 data). The data layout is illustrated in file_layout_l4.jpeg. The data are provides as a 38x18 array. The 18th row provides the latitudes in degrees. The last column lists the altitudes in km and the day-of-mission (#18). The data are binned in geographic coordinates. The filenames are yyyyddd_snoe_uvs_daily_geo_v02.asc" where yyyy is the year and ddd is the day of year. /NO_daily_mag_ascii Same as /NO_daily_geo_ascii but now binned in geomagnetic coordinates The filenames are "yyyyddd_snoe_uvs_daily_mag_v02.asc". Files: 00readme.txt This file data_processing.txt Describes processing of data from Level 1 to 5. version2.txt Description of Version 2 changes SNOE_NO_netcdf.tar.gz Compressed file with all data files in netCDF format. netcdf.txt File format of netcdf files SNOE_NO_orb_avg.tar.gz Compressed file with all orbit average files in ASCII. SNOE_NO_daily.tar.gz Compressed file with all daily files in ASCII format. A brief description of the SNOE spacecraft and instruments can be found in the NSSDC Master Catalog at http://nssdc.gsfc.nasa.gov/nmc For help with the science instruments onboard the spacecraft, and descriptions of the orbit and trajectory, visit the SNOE website. http://lasp.colorado.edu/snoe/ For help with the data products produced by the spacecraft, and the Ultraviolet Spectrometer in particular, visit the SNOE Data website. http://lasp.colorado.edu/snoedata/ ================================================================ ================================================================ List of known anomalies in the data NOTE: these anomalies are not listed in any particular order A1: There are days with no data. The cause is one of two reasons. (a) The S/C was not able to deliver sampled data to Earth due to computer resets or ground station LOS. (b) The processing routines discarded the data that was sampled because of extra noise, S/C pointing errors, etc. A2: Daily average files are comprised of the average of all orbits made during a given day. On occasion, only one orbit's worth of data is 'averaged' into the daily average files. The day average therefore has a poor signal to noise (SNR) ratio. Day 1999.083 and 2000.044 (geo) are examples of this type of data. A3: yyyyddd 1998259 to 1998263 has the magnetic coordinates calculated using equations 3 and 39 of Fraser-Smith (Rev Geophys, 1987). This differs from the rest of the data that uses a CGM lookup table on a one degree geographic grid. A4: Partial data exists (missing latitudes) for numerous days. Note that this anomaly is usually removed by the processing that creates the L4 data. A5: PMCs are visible in the data. They typically appear in the northern hemisphere from May through August, and in the southern hemisphere from November through March. The location in the SNOE database is typically at 96.6 km, between 60 and 90 degrees latitude. Note that this is not necessarily the actual location of a PMC, only where it appears in this dataset. ================================================================ SNOE orbit in the southern hemisphere The SNOE spacecraft samples the southern auroral region during orbits 0 through 5 and 12 through 14 (inclusive). SNOE does not fly through the southern auroral region on orbits 6 through 11. This is due to the fact that the orbit does not take the spacecraft poleward of -82.5 degrees. ================================================================ List of hardware and software compatible with these datasets. This file is a list of computers that the SNOE dataset is known to work with. All processing has been done in the IDL language on various *nix machines. The lines in this file are the output of the IDL command: IDL> print, !version The SNOE dataset has been decoded and viewed on the following systems: { x86 linux unix 5.4 Sep 25 2000 32 32} { x86 linux unix 5.3 Nov 11 1999} { x86 linux unix 5.2.1L Aug 2 1999} { sparc sunos unix 5.4 Sep 25 2000 64 64} { sparc sunos unix 5.4 Sep 25 2000 32 64} { sparc sunos unix 5.3 Nov 11 1999} { sparc sunos unix 5.2 Oct 30 1998} { sparc sunos unix 5.0.2 Aug 19 1997} ================================================================ Acronyms used in SNOE documentation A.U. Astronomical Unit ADCS Attitude Determination and Control System http://lasp.colorado.edu/snoe/lib/ADCS.html Ap geomagnetic activity index C&DH Command and Data Handling processor http://lasp.colorado.edu/snoe/lib/CDH.html CDF Common Data Format http://nssdc.gsfc.nasa.gov/cdf/ CGM Corrected Geo Magnetic http://nssdc.gsfc.nasa.gov/space/cgm/cgm.html cm centimeter doy Day Of Year (1 through 366) F10.7 10.7 cm radio flux HCI Horizon Crossing Indicator http://lasp.colorado.edu/snoe/lib/ADCS.html IDL Interactive Data Language http://www.rsinc.com km kilometer LASP Laboratory For Atmospheric and Space Physics http://lasp.colorado.edu L1/2/3/4/5 Level One/Two/etc. data products from SNOE see PROCESSING.TXT, FILE_USAGE.TXT LOS Loss of Signal m meters mW milliWatts NCDF network Common Data Format http://www.unidata.ucar.edu/packages/netcdf/ NO Nitric Oxide nm nanometer NSSDC National Space Science Data Center http://nssdc.gsfc.nasa.gov p photon PMC Polar Mesospheric Cloud S/C Spacecraft sec second (time unit) SNOE Student Nitric Oxide Explorer http://lasp.colorado.edu/snoe/ SNR Signal to Noise Ratio SXP Solar X-ray Photometer http://lasp.colorado.edu/snoe/lib/instruments.html#SXP URL Universal Resource Locator (a web address) UTC Universal Coordinated Time UVS Ultraviolet Spectrometer http://lasp.colorado.edu/snoe/lib/instruments.html#UVS YYYYDDD A date format, Year Day-of-Year (January 1, 1998 = 1998001)