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Proceedings of 1st International Workshop
on Computer Science and Information Technologies (CSIT'99),
Moscow, Russia, January 18-22 1999. — MEPhI Publishing
1999, ISBN 5-7262-0263-5 Book of Abstracts.
(Eds. Ch. Freytag and V. Wolfengagen)
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Integrated Satellite Altimetry
Data Base: Organization, Data Base Management System and Application
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This Document in Format PDF
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S.A. Lebedev, P.P. Medvedev, Yu.S. Tyupkin
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The purpose of the project which was undertaken with support
from the Russian Basic Research Foundation (Project ¹ 96-07-89315) was
to set up an integrated satellite altimetry data base (ISADB), which would
include the results of altimetry measurements carried out by the Russian
GEOIK geodetic satellites and by GEOSAT, ERS-1, ERS-2 and TOPEX/POSEIDON
during the period 1985-1998 ISADB also includes supplementary information
necessary for the processing and interpretation of experimental data. The
functions of data processing and data visualization for the problem-oriented
study of the sea level changes of the world ocean, large inland basins
and for the determination of the detailed characteristics of the gravity
field of the Earth are realized by software, in addition to the standard
data base management system (DBMS)
The ISADB shall be loaded on the WWW server of Geophysical
Center and thus will be available in the Internet. We believe that the
the database will be useful for experts in differend branch of sciences
because the altimetry measurements, carried out by the GEOIK satellites,
have not been available before for the scientific community . The altimetry
data from other satellites have not been available for many russian specialists
also.
The Russian GEOIK program was started in 1985 to obtain a
system of fitted parameters of the Earth (EP-90) including fundamental
geodetic constants, geocentric reference system, and the parameters of
the figure and the gravitational field of the Earth. Initially, this Program
was carried out by the Topography Service of the Ministry of Defence of
the Russian Federation and was classified. In 1992 many aspects of this
program were declassified. The GEOIK satellites is placed on orbit approximately
1500 km high with inclination of 74 or 83 degrees. Ten satellites were
launched till 1996. They were equipped both with radio altimeters (RA)
and space-borne geodetic instruments including Doppler system, radio range
system, light signaling flash system, and laser corner reflectors. Doppler
system gives signals in coherent frequencies of 150 and 400 MHz twelve
hours a day to measure radial velocity; light controlling system produces
flashes to photograph the satellite against the stars; laser corner reflectors
of effective area of 0.024 square meters and relay reflect signals of a
ground-based laser ranger and re-emit signals of ground-based radio ranger.
Ground-based stations measure Doppler radial component of
satellite velocity with respect to the observation station with an error
of 1 - 3 cm/s, determine the satellite position by light flashes with reference
to the stars with an error of 1 - 1.5'', and measure distances to the satellite
by laser and radio rangers with errors of 0.5 - 1 and 1 - 2 m respectively.
A great amount of altimeter data which has geodetic applications and is
important for oceanographic and for global meteorological researches has
been collected during the period from 1985 to 1995.
The bulk of scientific results of GEOIK program includes
the model of geopotential of EP-90 up to the 36th degree and EP-200 up
to 200th degree, the improved coordinates of the geodetic network stations,
and the catalog of the geoid heights in the World ocean. A list of the
satellites, characteristics of their orbits, standard deviation of the
altimeter measurements and their operating time are given in Table 1.
Table. 1
Russian Satellite Altimetry Program GEOIK
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No Satellite
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Data Launch
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Inclination,
deg
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Period of active work
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Standard deviation,
cm
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Calibration correction,
m
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| 1 |
14.06.85 |
73.6 |
08.07.85 - 31.10.86 |
60 |
-17.0 |
| 2 |
11.02.86 |
73.6 |
03.03.86 - 28.03.86 |
140 |
-25.0 |
| 3 |
02.12.86 |
83.6 |
21.12.86 - 15.12.87 |
166 |
-36.5 |
| 4 |
19.02.87 |
73.6 |
09.03.87 - 12.10.87 |
105 |
-26.0 |
| 5 |
30.05.88 |
73.6 |
20.06.88 - 27.07.90 |
88 |
-22.9 |
| 6 |
28.08.89 |
73.6 |
18.09.89 - 26.09.90 |
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| 7 |
30.07.90 |
73.6 |
19.08.90 - 05.03.93 |
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| 8 |
10 01.93 |
73.6 |
10.01.93 - 23.07.93 |
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-29.79 |
| 9 |
December 1994 |
73.6 |
18.12.94 - 28.07.95 |
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-25.42 |
So called Geophysical Data Record format (GDR format) of
altimetry data is usually used for geophysical applications. The following
computation stages have been completed to transform initial GEOIK altimetry
data to the GDR format:
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calculations of the orbits of the satellites GEOIK satellite
orbits on the basis of tracking data which were obtained by observation
with stations located in the area of the former Soviet Union and Antarctic
region;
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preliminary processing of radar altimetry data including
corrections for reducing measurements to spacecraft center of mass, instrumental
delays, and tropospheric effects.
The gravitational field of the Earth, the attraction of the
Moon and the Sun, tides in the solid Earth, light pressure, atmospheric
resistance, precessions, notations, and poles movements were taken into
account for calculation of orbits.
To calculate orbits the model (EP-90) of gravitational field
of the Earth up to 36th degree was applied. The following parameters of
the ellipsoid EP-90 were obtained: a = 6378136; b = 1:298, 257839303. The
GDR format of satellite altimetry data of included in the database are
given in Table. 2.
Table. 2
ISADB Geophysical Data Records Format
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Item
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Bytes
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Parameter
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Description
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Units
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| 1 |
4 |
Time_UTC |
Universal Time Coordinated at the
begining 1985 |
sec |
| 2 |
2 |
Time_MS |
Complementary time |
10-3 sec |
| 3 |
4 |
Lat |
Latitude |
10-6 degree |
| 4 |
4 |
Lon |
Longitude |
10-6 degree |
| 5 |
2 |
SSH |
Sea surface height (SSH)
corrected on Instrumental, Wet and "Dry"
Tropospheric, Ionospheric and Electromagnetic
Bias correction |
10-2 m |
| 6 |
1 |
Nval_H_A |
Number of valid points for 1
second SSH |
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| 7 |
2 |
RMS_H |
Root Mean Square (RMS) range
SSH |
10-2 m |
| 8 |
2 |
H_Off |
Height offset to be added to
all SSH |
m |
| 9 |
2 |
dH_Inv_Bar |
Inverse barometer correction |
10-3 m |
| 10 |
2 |
H_MSS |
Mean sea surface height |
10-2 m |
| 11 |
2 |
H_Geoid |
Geoid height |
10-2 m |
| 12 |
2 |
GA |
Gravity anomaly |
10-4 gal |
| 13 |
2 |
H_EOT |
Elastic ocean tide |
10-3 m |
| 14 |
2 |
H_LT |
Loading tide effect |
10-3 m |
| 15 |
2 |
H_SET |
Solid earth tide |
10-3 m |
| 16 |
1 |
H_Pol |
Geocentric pole tide |
10-3m |
| 17 |
2 |
H_Lev |
Mean dynamic topography by
hydrological measurements |
10-2 m |
| 18 |
2 |
D_Ocean |
Ocean depth |
m |
| 19 |
2 |
SWH |
Significant Wave Height |
10-3 m |
| 20 |
1 |
WS |
Wind speed |
10-2 m/s |
| 21 |
1 |
Flag |
Flag |
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The specific feature of the satellite altimetry data bases
is that the information is recorded in the binary Hewlett-Packard or VAX
format, as the direct-access files inverted by time (the geodetic and exact
repeatable GEOSAT program), by time and satellite series (the GEOIK experiment),
by space (the intersection point bases), by exact repeatable cycles ( the
TOPEX/POSEIDON satellite), or by the numbers of orbital arcs (the ERS-1
experiment).
Software. The search and selection of data, stipulated by
the developed software, are oriented on the specific features of the structure
of satellite information. The search criterion is a logical construction
based on a single search attribute (the simple search criterion) and on
the combination of simple search criteria by the logical operations OR,
AND, NOT in order to organize the search by several attributes. Moreover,
a few additional virtual attributes of search are suggested: region, data
and time, season, cycle, the serial number of the satellite, and the orbit's
number. The attribute <region> allows to select the region of research
on a real geographical map with precision up to 0.1 sec. Since the time
in the data bases is given in seconds or in the number of days and seconds
from the start of the count, the virtual <data and time> parameter,
for the user's convenience, permits to give the time of measurement in
the usual terms: data, month, year, hour, minute and second. The attribute
<season> is designated for selection of a certain seasonal period of
time for the whole base. The presence of virtual attributes of search,
such as the cycle, the satellite series, and the number of the orbit, provides
accomplishment of automatic selection without involving the supplementary
data. The so-called map of search is compiled before the search by using
the selected criterion of a search on the basis of inverting the files
procedure. The map is a succession of the disk number for the multi-volume
data base, and the names of the files, which information satisfies, in
the first approximation, the given logic conditions of the search. This
procedure greatly increases the rate of search and selection. Moreover,
the system automatically requests the disk necessary for reading. We should
note that in the process of search and selection, the system operates only
with the disk numbers, the name of the files and the number of records;
consequently; the volume of the service file with the results of selection
is small.
The important peculiarity of the DBMS is the availability
of multistage selection of information. After completion of the first stage
of selection into the subbase1 and the analysis of the selected information,
we can undertake the search with previously selected data by using any
new or already existing criterion and store the data into the subbase-2.
After selection of information, the system allows copying of selected information
either in the symbolic format into the file, or in the binary format with
merging of the entire bulk of information within one data base. On this
step one can specify the parameters necessary for the next steps of processing.
One can also to conserve the binary format of distributive or to decode
the data if the data is output in the binary format.
The system allows to conduct simultaneous selection and copying
of information into the user's data base. This data base retains the inverted
structure of the initial CD-ROM. The system allows to display values of
parameters of selected records and to draw plots of selected temporal data
series without termination of the search mode.
The block of Express-analysis and preliminary data processing
allows to identify selected data with tracks of satellite, to determine
the type of these tracks (ascending or descending), and to check their
position in space. It allows also to display variations of any parameter
along the track, or on some part of it. The function of improvement of
the values of sea surface heights by introducing various corrections and
the function of visualization of these values as deviations from the reference
surface (for example, from the geoid in the dynamic topography of the ocean) are
realized in this block.
The space structure of the studied parameter is analyzed
by averaging the data on a selected grid at the knots or centers of its
cells with subsequent visualization of the obtained field in the form of
isolines; an opportunity is provided, by analogy with the previous statement,
to correct the values of heights of sea surface by introducing different
corrections, or by the display of deviations from the standard surface.
The research was undertaken with support from the Russian
Basic Research Foundation (Project No 96-07-89315).
© Geophysical Center RAS, 1999 |