Auroral Imaging Digital Data from the Spin-Scan Auroral Imager (SAI) on Dynamics Explorer-1

The DE-1 auroral image data set consists of all mission analysis files (MAFs)
generated at the University of Iowa. Each MAF contains one nadir-centered image
produced by one of the three photometers. The angular dimensions of a typical
full frame are 30 X 30 degrees and span 14,400 pixels. The images from all
three photometers are telemetered simultaneously with a repetition rate that
can vary from about 3 to 12 minutes. Two of the imaging photometers provide
images of the earth at visible wavelengths via interference filters mounted on
a wheel and selected by ground command. Auroral images are obtained at 391.4,
557.7 and 630.0 nm. Several background filters are also provided. In
addition, filters at other wavelengths are included, such as those at 317.5
and 360.0 nm for measurements of the global distributions of ozone. Each
photometer is capable of observations with any one of a set of twelve filters.
The third imaging photometer is equipped with filters and a photocathode for
observations at vacuum-ultraviolet wavelengths, in particular emissions of the
Lyman-Birge-Hopfield band of molecular nitrogen at about 140 to 170 nm.
Imaging at these wavelengths will allow coverage of the auroral oval in both
the dark and sunlit ionospheres. The filter array for the vacuum-ultraviolet
imaging photometer also includes filters for atomic hydrogen Lyman alpha at
121.6 nm and oxygen lines at 130.4 and 135.6 nm.

An image is made up of all consecutive scans of the photometer without a
change in mirror stepping direction. Each MAF contains a header record
giving universal time, instrument parameters, and orbital position, followed
by a record for each scan line giving UT, mirror position, and pixels for
that scan. Each scan line record contains pixels collected by one photometer
during one six-second spacecraft spin. Each MAF contains all scans by one
photometer between changes of mirror stepping direction, up to 120 scans or
12 minutes per file. The same filter will normally be in use for the entire
image.

The data obtained in one operations period of the spacecraft are summarized
in three 35-mm slides, one for each photometer. These survey data were
designed to assist in monitoring instrument performance, to identify imaging
geometry, and to monitor the general state of auroral activity. They are NOT
designed for quantitative analysis.

A collection of lists and user information exists on IOWASP and includes the
following:
1) a list of telemetry data at Iowa,
2) a list of all MAFs that have been produced, accessible in data time
order or in MAF name order,
3) a list of spacecraft commands in time order, and access to expanded
explanations for most commands,
4) specific MAF formats, and image display and pixel-to-kilorayleigh
conversion information,
5) a graphic display option for DEC/Regis terminals showing the imager
view of the Earth for an input time.

The catalog is online at IOWASP on SPAN in a captive account for qualified
users. It may be accessed through SPAN by issuing the command SET HOST IOWASP
and replying SAI to the request for Username. The catalog may also be
accessed through the LINK command, if available in this directory.

PI-provided MAFs for the time period 1981-09-23 to 1987-02-05 and software
to access and display the images are available from NSSDC (81-070A-03A). The
data and software are stored on 3 optical disks and can be also obtained
through NSSDC's Automated Retrieval Mail system (NDADS-ARMS) as described in
the NMD entry on "On-line DE-1 Data Available via NSSDC's NDADS System".

NSSDC has developed an additional program to convert SAI data to
Common Data Format (CDF). An imaging/mapping tool (CXIT for Suns, CMIT
for Macs) for reading and displaying the CDF images was also developed
by NSSDC and can be retrived from NSSDC's anonymous ftp site at
nssdca.gsfc.nasa.gov in directory GRAPHICS_SOFTWARE; please consult
the directory SPDS/DE-SAI for the required CDF software.