A Description of the ASTER
Each day the ASTER Ground Data System (GDS)
in Japan analyzes the database of requests for ASTER data acquisitions and develops a
schedule for 27 hours of observations. This process is described here.
Requests for ASTER data acquisitions
Authorized individuals ("ASTER Users") and the ASTER
Science Team as a whole can request that the ASTER instrument acquire
new data. A request from an individual
ASTER User is called a Data Acquisition Request (DAR). A request from the entire ASTER
Science Team is called a Science Team Acquisition Request (STAR). The term "xAR"
is used to refer to either a DAR or STAR.
DAR and STAR input parameters
Each xAR describes the area which should be imaged (the "Area of Interest" or
AOI) and the epoch(s) during which such images should be acquired (the "Acquisition
Window(s)"). A variety of other parameters are specified for the requested
observations, including the maximum amount of cloud cover the requestor will accept in
his/her images and the desired ASTER observing mode.
- Different combinations of ASTER telescopes can be turned on for different observations.
Each combination is called an observing mode. One can request that data be acquired by:
- TIR, SWIR, and VNIR telescopes
- Most daytime observations will be acquired in this mode.
- VNIR acquires stereo images by recording nadir and back-looking data (at
810 nm) for an extra 60 seconds after a target has left the nadir field of view.
- TIR and SWIR telescopes
- TIR telescope
- Most nighttime observations will be acquired in this mode.
- VNIR telescope (includes 810-nm stereo data)
- VNIR 810-nm channels only (stereo)
This website provides online help in choosing values for some of xAR input parameters
Helpful hints on xAR input parameters. More
information on all input parameters is provided in the
Tool User Guide.
The DAR Tool will enable ASTER Users authorized by NASA to submit their requests
to the ASTER GDS. STARs will be submitted by the Science Team to gather larger amounts of
data, usually of general interest to the science community. At the GDS, DARs and STARs are
collected in the "xAR database," which is used as input whenever a One Day
Schedule is generated.
The ASTER Scheduler
The ASTER GDS contains software (the ASTER Scheduler) which chooses between different
observing alternatives for each small increment of time, in a manner designed to maximize
the science return over a time period of a day. The Scheduler reads all active DARs and
STARs in the ASTER GDS in order to do this. Its scheduling algorithm uses a prioritization
function to rank the alternative observing modes (and non-observing instrument modes) for
each time-step. The output schedule can be modified by changing the Schedulers input
parameters; the ASTER Science Team is responsible for choosing these input parameters.
The latest global cloud-cover forecast from NOAA is used as input by the Scheduler
each day, when generating the One Day Schedule. These data are used in the prioritization
function to increase the fraction of ASTER images which are sufficiently free of clouds to
meet the requirements of ASTER users.