readme

根据GPS观测数据

This directory contains all the files of an example run of the programs
IonoBias and TECMaps, including scripts and output.

Program descriptions

   Program IonoBias reads Rinex data files containing extended Rinex observation
types EL, LA, LO and SR or SS (see preprocessing, below) from several sites and
estimates biases in the ionospheric total electron content (TEC) measurements
imposed by the hardware: either by satellite (the satellite + receiver combined
bias) or by receiver alone (average over satellites to get the receiver bias).
IonoBias does this by assuming a simple model of the ionosphere and
simultaneously estimating biases and model parameters.

   Program TECMaps reads Rinex data files containing extended Rinex observation
types EL, AZ and SR or VR from several sites and at each epoch fits the vertical
TEC data to a model of the ionosphere on a two-dimensional grid surface.
Hardware TEC measurement biases are corrected, using input from the program
IonoBias. The user can specify the type of grid, the type of TEC data and the
model to be used. Output is in the form of files, one per epoch, which can be
used to plot the 2D ionospheric TEC surface.

   Here is a description of the steps needed to go from raw data to plots using
these programs. You may have to change some directories or other small things in
the scripts, particularly the perl scripts, but this should be straightforward.
(Scripts may be used on Windows by renaming with .bat extension; you will need
perl and maybe wget and gnuplot under Windows -- get them free on the web!)

   0. Create subdirectories 'alldata', 'processed' and 'out'.

   1. The raw data is IGS data downloaded from the web for day 210 of 2004;
the script 'getigs' shows one way to do this using wget. Note the last 'wget' call
is different - it gets the broadcast ephemeris. These stations were
chosen because they lie near or within a rectangle bounded by latitude 40 - 60 and
longitude 250 - 290, which is where the map is going to be made. The raw data
files, including the broadcast ephemeris file, are placed in subdirectory 'alldata'.

   2. Preprocess the data by computing EL (elevation), AZ (azimuth),
LA (latitude of the ionospheric pierce point or IPP), LO (longitude of IPP), and
SR (slant TEC derived from pseudorange), using the Rinex tool ResCor
(see apps/Rinextools in the GPSTK distribution). A perl script, preprocess.pl
and a script which runs this for each data file, 'gopre', are provided here.
The ResCor run does several important things: it defines the data interval,
which for this data is 30 seconds, in the header, and it defines the 'MARKER NAME'
header record to be the 4-character station id in the file name (e.g. algo, chur,
etc.), it pulls out the receiver position from the input Rinex header and passes
that into ResCor, and finally it allows C1 to be used when P1 is not available.
It also summarizes the output file using program RinSum and puts this summary,
along with all the processed data, in subdirectory 'processed'.

   3. Run program IonoBias to compute the satellite+receiver biases for this
data; see the script 'gobias' which simply makes a file containing the names of
all the preprocessed data files (or you can make it by hand), and then runs
IonoBias with the input file bias.inp. Output of this program is in bias.log,
and the biases are also put in the file satbias.txt that will be input to TECMaps.

   4. Run TECMaps using the script 'gomaps', which simply runs TECMaps using the
input file maps.inp, which chooses the grid type, the model type and the output
format. Output is placed in subdirectory 'out' with base name 'igs' (i.e. all
the files are of the form 'igs.N' where N is the epoch number: 1-2880 (an entire
day of 30 second intervals).

   5. View the output using gnuplot. The perl script plotall.pl will generate an
input file for gnuplot and run it, or use the script 'see'. Again, you may have to
change directories inside plotall.pl; there are other options that fix how the
plot is done, including output to a file (.png) instead of to the screen.
For example, type
      ./see igs 1 2880 30 
to see plots of the VTEC map every 15 minutes (30 x 30sec) from the first to the
last. Press 'return' in your terminal window to advance to the next plot.