The Dynamics Explorer (DE 1 and 2) satellites were launched August 3, 1981 by a Delta rocket from Vandenberg Air Force Base. The two satellites were placed into coplanar polar orbits to collect data on the magnetosphere, the ionosphere, and the upper atmosphere. The DE-1 satellite was in a highly elliptical orbit with an inclination of 89.9 deg and a period of 6 hr 49 min. The magnetometer was mounted on a 6 m boom. DE-1 collected data through 1991; however, DE-2 at a lower initial altitude reentered the atmosphere in 1983. DE-1 was spin stabilized with the Z axis of the satellite (also the spin axis) antiparallel to the orbit normal and equivalent to Bphi. The X and Y satellite axes complete a rotation every 6 seconds and correspond to Btheta and Br axes of the magnetometer [Hoffman, 1981].
The DE 1 and 2 data reside on optical platters and are maintained by the LEP (Laboratory for Extraterrestrial Physics) at NASA's GSFC. The DE-1 datasets are relative to Geomagnetic Spherical (GMS) coordinates based on the magnetic dipole (Br is positive radially outward from the Earth, Bphi is positive toward the east, and Btheta completes the right hand system). There is no statistical attitude information available so only the computed total field data are of use.
The following is an outline of a project conducted on DE-1 data at the Goddard Space Flight Center in 1995. The programs and datasets referenced are included on CD: DE101 where available. Some name changes were made to account for the difference in PC and UNIX naming conventions:
/LEV1/
bl1 = de18190.bin.lev1
bl10 = de18190.bin.lev10
de.ob = de18190.de1bq20the.obsbin
de.nb = de18190.de1bq20the.nobsbin
d.ob = de18190.de1bq20th.obsbin
d.nb = de18190.de1bq20th.nobsbin
el10 = de18190.epltxbq20th.lev10
el10e = de18190.epltxbq20the.lev10
el10.ssm = de18190.epltxbq20th.lev10.ssm
el10e.ssm = de18190.epltxbq20the.lev10.ssm
deone.nob = deone.noobs.dat
deone.obs = deone.obs.dat
/PROGRAMS/
quiet_de = quiet_de1
gsfc1187 = uned.gsfc1187
bq20th = uned.bq20th.igrf
newfit_e.f = newfit_eplt.f
The DE-1 data were copied from optical disk onto disk space on the Eldyn2 Vax. Read_de1.for was then applied to the daily files for which the average Kp for the day was < 18. (These days are listed in /programs/quiet_de, output from /programs/kpap_jd.f)
/programs/read_de1.for
Purpose: Reformat original DE-1 files in unformatted Vax binary to acsii. Select points based on:
1. lat and lon < 9999 nT
2. alt ,<= 1000 km
Input Format: raw binary (DE1R)
Output Format: processed ASCII (DE1P)
The data files output from this program are:
/lev0/agmsYRDY.rat
for YRJD ranging from 81260 - 90317. Three processing programs (de1form.f, dstadd.f, smooth.f) were then applied to the data with /programs/de1form.sc. The output from these programs was merged with the UNIX ``cat" command and is stored as:
/lev1/bl1
/programs/de1form.f
Purpose: Reads the ASCII files output from read_de1.for then converts the position information from GMS dipole coordinates to geocentric Earth-fixed coordinates
Input Format: processed ASCII (DE1P)
Output Format: newfit binary (BIN)/programs/dstadd1.f
Purpose: Adds Dst values to the data
Input Format: newfit binary (BIN)
Output Format: newfit binary (BIN)/programs/smooth.f
Purpose: Uses subroutines from Numerical Recipes to add a smoothing filter through a fast Fourier transform to each pass thereby removing the spin tone present in the computed scalar B data through the following steps:
1. checks for passes with gaps > 60 sec
2. calculates field values from a model (uned.gsfc1187)
3. eliminates points for which Bmeasured-Bcomputed > 200 nT
4. forms a smoothing filter based on residuals
5. adds pad values to the end of the pass
6. performs the FFT
7. adds the field values back to the corrected residuals
8. writes the data out with the BM(10) variable replaced by the smoothed value
Input Format: newfit binary (BIN)
Output Format: newfit binary (BIN)
The file /lev1/bl1 was then decimated with decimate.f generating the output file /lev1/bl10.
/programs/decimate.f
Purpose: decimates the data by selecting every 10th point
Input Format: newfit binary (BIN)
Output Format: newfit binary (BIN)
The data were then reformatted and field values added with newfit_e.f
/programs/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)
Two sparse datasets (/lev1/deone.nob and /lev1/deone.obs) were created separating the data into a file coexisting with observatory data (nob) and a file with data not in an observatory bin (obs). Bins were assigned by dividing the Earth into 92 equal area sectors. Computed values were then added to these files with compare.f based on the GSFC spline model from which the GSFC IGRF95 candidate model was extracted (/programs/bq20th equivalent to uned.bq20th.5q10.1q11.1s11.igrf). Output files are:
/lev1/de.ob (used external model info)/lev1/de.nb (used external model info)
/lev1/d.ob (did not use external model info)
/lev1/d.nb (did not use external model info)
/programs/compare.f
Purpose: Compute field values based on a model and replace the existing value
Input Format: DE1S
Output Format: DE1S
A scaling technique was used with these files in an attempt to reduce a 20 nT bias between the data and the main field model [Langel et al., 1996]. This analysis used an iterative least squares technique to estimate data scaling components along and normal to the spin axis. These scale factors computed from the sparse dataset were then used to adjust the X:Y and Z components and recompute B in the large 1/10th dataset. This data was then smoothed. Both of these steps were executed by scsmooth.f which was invoked by scsmooth.sc. The output files were:
/lev1/el10.ssm
/lev1/el10e.ssm
/programs/scsmooth.f
Purpose:
1. applys the scale factors to X:Y and Z
2. recomputes Bmeasured from X, Y, Z
3. follows the smoothing steps listed above for /programs/smooth.f using the field information already included on the tape
Input Format: extended plot binary (EPLTX)
Output Format: extended plot binary (EPLTX)