Wind and Temperature Intermediate Data from the Wind and Temperature Spectrometer (WATS) Experiment on Dynamics Explorer-2

The Wind and Temperature (WATS) experiment on the Dynamics Explorer-2
(DE-2) spacecraft consists of a closed source neutral mass
spectrometer with two rectangular baffles which are swept across the
incoming neutral beam. The modulation of the neutral flux by the
baffles allows measurement of the temperature and gas velocity. The
mass was commandable and was usually selected to be N2 or O.

The data set consists of neutral density temperature and vertical and
zonal winds for atomic mass number 28 and 16 (measured as 32). One or
two of these masses may be measured at the same time, but any
differences in the temperature or wind is thought to be due to
experimental error with the greatest error in the mass 16
measurements.

The data are called 'intermediate' because there are corrections that
need to be applied in order to produce a final data set. The
corrections are not fully understood at this time and new corrections
may sometimes be necessary. The value of the intermediate data set is
that it contains the original data without any loss of resolution and
it may be used, as is, for spectral analysis and by other
investigators who have already included in their programs some of the
correction factors. When new correction factors are calculated they
are sent to investigators instead of sending a new data set.

Each record in the data set consists of 11 4-byte words in binary format as
follows:

WORD TYPE CONTENTS
1 integer julian date
2 integer time in milliseconds
3 integer mode (3 or 4)=horizontal (5 or 6)=vertical
4 integer out/in flag 1=baffle going out 2=baffle going in
5 integer mass in amu - usually 28 or 32
6 real number density (number/cc)
7 real temperature (deg k)
8 real velocity (m/s) spacecraft coordinates
9 binary engineering bits
10 binary engineering bits
11 real velocity (m/s) geographic coordinates

The resolution is 2 4 6 or 8 seconds depending upon how many of the
two second measurements are repeated in the eight second measurement
cycle. A routine mode was two horizontal and two vertical
measurements which would give a time spacing of 2 6 2 6 2 6
.... seconds for the velocity and a resolution of 2 seconds for the
temperature which is obtained from both baffles. For higher time
resolution in density and composition information the DE-2 NACS
measurements should be used.

The error in the temperature is about 3% at an altitude of 250 km and
it increases with altitude proportional to the inverse of the square
root of the density of the mass being measured. Since the error
increases as the atmospheric density of the measured gas decreases,
the mass was usually selected to be the dominant species. The error
in the velocities is about 10 meters/second at 250 km with the same
altitude dependence as in the temperature. In addition to this
statistical error, there is an uncertainty of about 24 meters/second
in the velocity due to errors in angle sensing of the baffle arm.

The original version consists of data in the DE Sigma-9 tape library
with the velocity in spacecraft coordinates. A data tape contains one
file per satellite pass and is unsorted in time. The version
described here contains velocities in geographical coordinates and is
sorted in time.

For more information, background and access to data, see:
http://nssdc.gsfc.nasa.gov/space/

The three PI-generated WATS data tapes are available from NSSDC
(81-070B-04C). In addition NSSDC distributes the DE-2 Unified Abstract
(UA) tape which includes data from the NACS, WATS, LANG, FPI, RPA and
IDM instruments at 16 second time resolution (81-070B-04D). The
orbit/attitude files and associated software are included on the UA
tape, but not on the MAF tapes.

The variability of thermospheric and ionospheric parameters measured
by NACS, WATS and LANG is illustrated in a computer generated movie
that is available from NSSDC on video tape (81-070B-04A) or on 16mm
film (81-070B-04B). See:
http://nssdc.gsfc.nasa.gov/