Document title: Format description for NDADS DE IDM_ASCII datatype
Project: DE
NDADS Datatype: IDM_ASCII
Super-EID: DOCUMENT
There may be other documents also identified by this super-EID.
NDADS filename: IDM_READ_ME_DE.DOC
TRF entry: B46558.txt in NSSDC's controlled digital document library, Feb. 1998.
Document text follows:
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DE-2 Ion Drift Meter data on NDADS
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The Dynamics Explorer 2 Ion Drift Meter (IDM) ASCII files contain
mutually perpendicular ion drift velocities in spacecraft coordinates
and the most important DE-2 orbit parameters. NSSDC-developed software
was used to read the IDM binary data and create ASCII files. For more
on DE-2, IDM, and the binary data, see IDM_VOLDESC_DE.SFD and
IDM_FORMAT_DE.SFD.
The IDM files are requested with the DATA_TYPE = IDM_ASCII and the
ENTRY_ID = yyddd and are then staged as yydddhhmm_IDM_DE_250MS_V01.ASC;
yy is the year, ddd is the day of the year, hh is the hour, and mm is
the minute of the starting time of the data in the file. The date range
for the IDM files is 81227-83047 (08/15/81-02/16/83) with most days
represented.
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Format of yydddhhmm_IDM_DE_250MS_V01.ASC Files
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Each data record contains the following data. If there is no data for
a given parameter, the field is filled with 9999999.0.
date (yyddd)
UT (ms)
geographic latitude (deg)
geographic longitude (deg)
invariant latitude (deg)
magnetic local time (hr)
altitude (km)
spacecraft velocity (m/s)
number of time/velocity pairs (n)
time of ion velocity measurement #1 (ms)
ion velocity measurement #1 (m/s)
...
time of ion velocity measurement #n (ms)
ion velocity measurement #n (m/s)
Each data record spans several lines in the ASCII files. The first line
of each record contains the following data: date, UT, geographic latitude,
geographic longitude, invariant latitude, magnetic local time, altitude,
spacecraft velocity, and the number of time/velocity pairs. The remaining
lines contain the time/velocity pairs, with 6 pairs on each line.
The ion velocities are given as REAL numbers. But only the INTEGER part
(digits to the left of the decimal point) gives the actual ion velocity
measurement. The two digits to the right of the decimal point are not
data values, but indicators of the velocity direction, the data quality
and the specific sensor. The first digit after the decimal point
provides a density-dependent quality flag:
0 or 1: good
2 or 3: averaging over several data points is recommended
4 or 5: data are unreliable
The second digit after the decimal point indicates the direction of
the velocity measurement. If the digit is even then the velocity was
measured along the z-axis in spacecraft coordinates (approximately
horizontal). If odd the direction is along the spacecraft y-axis
(approximately vertical; positive for upward velocity) (y). Please see
the IDM_FORMAT_DE.SFD file for a complete description of these indicators.