The POGS satellite was launched on April 11, 1990 from an Atlas launch vehicle and collected data through 1993. It was managed through the Naval Oceanographic Office (NAVO) who operated the satellite and collected and processed the data. It was in a circular polar orbit of approximately 700 km at an inclination of 89.99 deg. A triaxial fluxgate magnetometer was mounted on an eight foot Earth-pointing boom. The spacecraft was gravity gradient stabilized; however, it was inadvertently deployed upside-down causing problems with the solar panels and telemetry antenna. The magnetometer clock also suffered as much as 5.5 seconds of drift from Greenwich Mean Time (GMT).
The 10-day processed files reside on /data/lev1 in yearly tar files. Use the Unix command `tar -xvf tarfile' to explode these data. These files (pogsYSTD.dst) where Y=year-1990, STD= start day, EDD= end day, were downloaded from NAVO using ftp. The processed data have been calibrated, adjusted for thermal drift, merged with ephemeris data, have had the initial time-error correction applied, and have had the Dst index included with each observation [Quinn et al., 1993]. These data are in geocentric Earth-fixed coordinates. Although the instrument measures vector components, no attitude control was available. The satellite sampled data once every second, but because of a software glitch, measurements are only available once every ten seconds.
Unprocessed data files (/baldwin/data/jan92/rawdata.tar) for January 1992 were also obtained along with ephemeris data (/baldwin/data/jan92/pYSTDEDD). Source code (/baldwin/source/pogsmrg.c) was obtained from Don Shiel of NAVO. The code applies all of the NAVO corrections.
The original POGS 10-day files are in /data/lev1. These files were processed with /baldwin/source/pogsform.f to remove data > 2+ Kp, remove data -50nT < Dst < 40nT, compute latitude and longitude from geocentric Earth-fixed coordinates, remove points flagged as outliers, and remove points when the satellite beacons are activated. None of the data have had any of John Quinn's timing correction or drift correction applied. /baldwin/source/pogsfor1.f was then used to convert the data to newfit ASCII (ASC). The output files are:
/data/lev2/pogs1001.xyz
/data/lev2/pogs3001.xyz
/baldwin/source/newtbin.f was then used to convert the files to newfit binary (BIN) format:
/data/lev2/pogs1001.bin
/data/lev2/pogs2001.bin
/data/lev2/pogs3001.bin
The data were then reformatted and field values added with /source/pogsplt1.sc which invoked newfit_e.f. The model used was the Goddard spline model used to extract the GSFC IGRF95 candidate model (/data/uned.bq2 in UNED format equivalent to uned.bq20th.5q10.1q11.1s11.igrf) - the external field coefficients included with the model were not used.
/source/newfit_e.f
Purpose:
1. adds Bcomputed and residual values based on a model
2. adds orbit number based on time
3. computes dipole latitude, magnetic local time, local time, and orbit latitude based on E-N-E-S-E format
4. assigns bins based on longitude and Dst
5. rejects points for Bmeasured - Bcomputed < 200 nT
6. rejects passes that are < 40% complete (200 pts)
Input Format: newfit binary (BIN)
Output Format: extended plot binary with Bcomputed replacing Xresid (EPLTX)
output files from this program were:
/data/lev3/pogs1001.lv2
/data/lev3/pogs2001.lv2
/data/lev3/pogs3001.lv2
Quiet days were then selected based on the average Kp values for each day. The Kp for the POGS data was written out using pogs_dis.f with the following output files:
/data/lev3/pogs91.out
/data/lev3/pogs92.out
/data/lev3/pogs93.out
/source/pogs_dis.f
Purpose: to write out the average daily Kp information for each POGS data point
Input Format: newfit binary (BIN)
Output Format: listing
From this list, the following quiet days were selected:
January 14-23, 1991
March 11-16, 1991
March 18, 1991
May 11-21, 1991
January 18-26, 1992
February 13-16, 1992
April 10-17, 1992
June 1- 6, 1992
July 3-10, 1992
August 30 - September 1, 1992
January 21-24, 1993
February 23-27, 1993
April 28 - May 13, 1993
May 21-25, 1993
May 30 - June 22, 1993
July 12-18, 1993
These dates were extracted from the processed POGS dataset using pogs_sha.sc which executed shavYJDY.f for each of the three datasets.
/source/shavYJDY.f
Purpose:
1. select points within the date ranges listed above
2. select points with hourly Kp < 23 (based on closest 3 hr Kp block)
3. select points with -20 nT < Dst < 5 nT (based on Dst values included with each point)
4. separate the output into points within a 2 degree bin with an observatory and those points in a bin with no observatory
Input Format: extended plot binary with Bcomputed in the place of Xresid (EPLTX)
Output Format: extended plot binary with Bcomputed in the place of Xresid and Kp in place of Yresid (EPLTX)
The output files are in:
/data/quiet/pogsYJDY.b# (binned)/data/quiet/pogsYJDY.nb# (not binned)
Refer to Langel et al. [1996], for an error analysis of scale factors, offsets along each measurement axis, and non-orthogonality between the magnetometer axes.