Unified Abstract (UA) Merged Mission Data

Description

Provided by the project office, this data collection contains data from most of the Atmosphere Explorer-D investigations. The data were originally provided on binary magnetic tapes written on an XDS 930 computer, each tape containing several calendar months of data.

The first file of the tape is a header file specifying the satellite ID, point-by-point data record size, start and stop times of the data contained on the tape, a list of orbit numbers on the tape, and the magnetic and solar activity data for the time period. Subsequent data files, called "UA" files (Unified Abstract files), contain one orbit of UA data and orbit data, and are arranged in ascending order by orbit number. Each data file consists of a header record followed by approximately 145 records. The header record contains the orbit number, orbit start and stop times, UA header data, and orbit parameters corresponding to that orbit. The data records contain UA and orbit data at 15-s intervals for the time span specified in the header record. Since there may be gaps in the data, each record contains a corresponding time.

The results from the Cylindrical Electrostatic Probe (CEP) experiment are contained in record words 58-60 and are, respectively, the electron temperature, the ion density, and the satellite potential. These words are stored as floating point numbers.

Results from the Low-Energy Electrons (LEE) instrument can be found beginning with word 62. Values are given for the following: total energy flux for electrons in the energy ranges (keV) 0.2-0.8, 0.8-2, 2-7, and 7-27; average energy for electrons; total electron flux; total energy flux for ions; average energy for ions; and the total ion flux. The data are condensed using data from 7.5 s before and 7.5 s after the 15-s time mark, making available 15 stepping sequences for processing. When the spacecraft was in a 15-s spin mode, only data from the upper hemisphere are accepted.

Data from the Atmospheric Density Accelerometer (MESA) experiment are contained in words 71 and 72 and are, respectively, density in g/cc and wind in m/s.

The data from the Magnetic Ion Mass Spectrometer (MIMS) are found beginning at word 73. The measurements give values for the ion concentrations (ions/cc) of the following ion species: H+, He+, N+, D+, N2+, NO+, O2+, O++, O+, and Mg+.

Measurements from the Neutral Atmosphere Composition (NACE) experiment begin with record word 83. The data include values for the concentrations (number/cc) of the following neutral atmospheric species N2, O, He, Ar, NO, and the equivalent total O from (O + 2xO2). The 10 least-significant bits of each of these six words provide an estimate of the fractional error.

Data from the Neutral Atmosphere Temperature (NATE) instument start at word 89. Values are given for the following parameters: the neutral gas temperature; the concentrations (number/cc) of N2, equivalent total O from (O + 2xO2), He, Ar; vertical motions; and horizontal (normal to the orbit plane) winds. These measurements are all represented as floating point numbers. Whenever any one of the values is not being measured, a zero is inserted.

The data from the Open-Source Neutral Mass Spectrometer begin with record word 96. The data include the concentrations of the following neutral atmospheric species (number/cc), respectively -- N2, O2, He, O, Ar, N, and a value for the equivalent O2 from (O2 + O/2). In all seven words, the eight lowest order (rightmost) bits have been replaced with a percentage error byte. Masking off these bits gives directly the percentage error of the data value.

Data from the Photoelectron Spectrometer (PES) instrument are contained in the six data words beginning with 102. The normal energy ranges included are as follows: 2-3, 7-9, 12-17, 25-30, 37-40, and 100-500 eV. In some operating modes, only a partial sampling of the full 1-500 eV energy range was obtained. A portion of the data has zero values in all but words 106 and 108. In this case, word 106 contains the average flux from 7-42 eV and word 108 contains the average flux in the 100-500 eV range. In all cases, the data reported are a 15-s average of the flux for the interval beginning with the time associated with the data word.

Data from the Retarding Potential Analyzer/Drift Meter begin with word 109. The outputs include ion temperature (deg K), total ion concentration (ions/cc), ion drift velocity along the +/-X axis of the spacecraft (m/s), vehicle (ground plane) potential (V), total ion concentration roughness (percent), the ion drift velocity along the +/-Y axis of the spacecraft (m/s), the ion drift velocity along the +/-Z axis of the spacecraft (m/s). The RPA and duct data are obtained every 15 s from 30-s running weighted averages of the individual data points. The drift meter data are represented by the individual data point nearest to the time indicated. In this case, the time difference between the data point and the time indicated is usually less than 2/3 s.

Results from the Ultraviolet Nitric Oxide experiment begin with data record word 118. Values are given for the following parameters: the NO scale height and NO density at the spacecraft altitude, the NO density at 150 km, the maximum NO density observed during a given scan, and the altitude at which this maximum occurred.

Data record word 123 begins the Visible Airglow Photometer (VAE) data. The values are obtained every 15 s by linearly interpolating data taken on either side of the 15-s point. For each orbit, the VAE stores two header records in addition to the data. The first header is a 9-word record giving orbit number and investigation status. If the status word contains "dual", the VAE changes mode in the pass. The second header record defines both modes, which are related to the wavelengths observed as tabulated in the appendix of a format document available from NSSDC. In addition to identifying the two wavelengths being measured, the second header record describes for each of the six data words, whether the data are from channel 1 (narrow field-of-view) or channel 2 (large field-of-view), and the direction the instrument was looking when the data were collected.

Some of the other parameters included in each record are date and time of the measurement; time from perigee; sunlight/darkness flag; Greenwich sidereal time; height above the geoid; satellite position and velocity; geodetic latitude of the subsolar point; east longitude of the satellite; local apparent solar time; local magnetic time; McIlwain's L-shell parameter; invariant latitude; magnetic field strength; and geodetic latitude and longitude of both the ingress and egress points of the geomagnetic field line through the satellite.