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Space monitoring of a condition of water objects. / December 4, 2008 /

The tasks relevant to resource management and analysis are best addressed by using of remote sensing data and operative environmental monitoring.
Extreme natural phenomena like flooding, inundation, and shoaling of lakes and reservoirs rarely occur however their pending is rather progressive and even minor changes in the natural environment or in man-made environment may trigger them.

The prediction of water body behavior is based on the analysis of their hydrological models and taking account of data on weather conditions, water stage and discharge. Satellite systems with a high revisit possibility and over a short period of time may provide the data required for determining the model parameters describing the hydrological features and watershed of a territory, watershed topography, vegetation types and extent, soil types, bedrock types, etc.

Satellite data in combination with in-situ reference data allow for constructing more accurate and composite hydrological models than that constructed using ground-based measurements only and were of linear character. Such an approach enables using the distributed physical model of hydrological system and refining the technique of its use.

The hydrological model parameters are determined using data from multiple sensors and satellite systems that collect imagery in different ranges of the electromagnetic spectrum and with different spatial resolution. Mapping of vegetation extent and composition is feasible using multispectral low and moderate resolution imagery data. And just the same is true for land use and soil type determination. The topography, geology, and geomorphology of river and lake drainages are studied using high and very high resolution optical and IR imagery data and radar data as well. Since optical imagery data have some limitations because of cloudiness then a combined use of multisatellite data is an optimal approach.

The requirements for satellite systems providing data needed for constructing hydrological models are listed in Table 1.

Table 1

Parameter

Resolution (m)

Observing Frequency

max

min

optimal

max

min

optimal

1.

Topography

1

20

10

Every two years

Every five years

Annually

2.

Vegetation Types

10

150

20

Monthly

Every three months

Every two months

3.

Land Use

10

150

20

Every three months

Each half year

Each half year

An operative satellite monitoring of inland reservoirs requires a continuous analysis of data on weather conditions, water stages and discharge from hydrological ground networks and an analysis of remote sensing data underwent processing as well.
In studying the stream-flow regime of land and in predicting flooding, the reservoir surface area is one of the essential input parameters of hydrological models. To extract information on the given parameter from in-situ data is a complicated challenge and requires numerous measurements. Satellite data enables this problem to be simplified substantially.
To this end there has been developed a specific technique of water surface monitoring allowing for satellite data-based estimation of water surface area and generation of water surface maps on a regular basis. One example of the use of this technique at the Research Center for Earth Operative Monitoring (NTs OMZ) is the estimation of the Aral Sea water surface.
The ecological catastrophe occurred in the Aral Sea in the latter part of the twenties century comes to the attention of scientists and ecologists of the world and demands a regular monitoring of the reservoir. Because of uncontrolled diversion designed for irrigation in Central Asia and Kazakhstan in the 1950s and 60s, the runoff to the Aral Sea decreased dramatically and in the 1980s stopped. In 1961 the total are of the Sea was 66 thousand sq km, the change in water stage through evaporation was about 1 meter during the year, this change was not compensated for stream flows, and since 1961 till 1990 the water stage decreased by 14.8m.
Currently, the Aral Sea left behind only three reservoirs, in two of which the water became so much salted (more than 100%) that no fish exists there. The regressed sea left approximately 58 thousand sq km of dry sea-bed covered not only by salt, but in places by sediments of various weed and pest-killer chemicals washed from neighboring fields. The sea-bed exposed was named „Desert of Aral-Kum“. At present strong storms scatter salt, dust, and weed and pest-killer chemicals through a distance of about 500km. The airborne sodium chloride, sodium bicarbonate, and salt cake inhibit the growth or wipe out vegetation and agricultural crops. The inhabitants suffer from respiratory diseases, throat and esophagus cancer, anemia, indigestion. The diseases of kidneys, liver, and eyes became more frequent.
In 2001 as the result of desiccation the Vozrozhdeniye [Renaissance or Rebirth] Island has been connected with the mainland. According to some sources, in the epoch of the Soviet Union the Island was chosen for open-air testing of biological weapons using animals (tularemia, agents of anthrax, plague, brucellosis, typhus, smallpox etc). This is the reason for concerns that pathogenic microorganisms would survive and infected animals might be their disseminators to other regions.
At the NTs OMZ the dynamics of change in the Aral water surface area was studied using multiyear satellite imagery data acquired and processed by the Center. The RESURS-O1/MSU-SK and MODIS/Terra images taken over the period 1993-2008 have been used for the studies. Table 2 gives the main characteristics of the instruments.


Table 2

RESURS-O1/MSU-SK

MODIS/Terra

Swath Width, km

700

2330

Number of Channels

6

36

Spatial Resolution, m

160

250-1000

Radiometric Resolution, bit

8

14

The images used for monitoring of variation in reservoir water surface fall on summer period (July, August) except for images acquired in 2003 and 2008 (May, October). Figure 1 shows some images of the generated time series.

For lack of the required satellite images taken before 1993, the 1:1000000 topographic map, the 1960s and 1:7000000 topographical map from the Officer Atlas, 1984 available at the NTs OMZ’s Fund have been used for mapping the Aral Sea surface.

The value-added processing of remote sensing data used involved the distinguishing of object classes referred to the sea water surface in multispectral image using a controlled classification of ERDAS Image program package, automatic calculation of water surface areas, and generation of end data products by means of GIS-package ArcGIS.

The end value-added product is a topographical behavior map of the Aral Sea surface that depicts changes in water surface area over the period 1960s-2008. The map contains data on water surface area and boundaries.


The map demonstrates the process of desiccation of the sea that has reduced by a factor of 6.5 in area over 48 years. This trend has been very fast in recent years. However the data given in Table 3 shows that the sea has widened in area by 346 sq km rather than reduced (from 18846 to 19192 sq km) during the period 16 August 2004 – 17 August 2005. The reason is most likely to be a powerful levee construction of 13km in length comprising concrete dam with regulating valve to control water discharge. Nevertheless, this has not stopped the shrinkage of the Aral Sea.

Below are given the results of estimating the dynamics of changes in the Aral Sea surface area.


Table 3

Date

Source

Area, sq km

% of the sea area in 1960

1960s

Topographic map of 1:1000000

68 900

100

1984

The Officer Atlas topographical map of 1:7000000

59 878

86.9

17 July 1993

RESURS-O1/MSU-SK image

36 182

52.5

7 July 2001

Terra/MODIS image

28 025

40.7

12 September 2002

20 687

30.0

1 May 2003

20 628

29.9

16 August 2004

18 846

27.4

17 August 2005

19 192

27.9

29 August 2006

15 479

22.5

12 July 2007

13 869

20.1

5 October 2008

10 579

15.4

The satellite data-derived behavior of reservoir water surface area contain rather valuable information required for specifying hydrological characteristics of the sea and enables estimating the water stage and determining the trends in water surface area using the water volume level. As the Aral water level lowered, its shoreline dramatically changed. The islands became peninsulas, archipelagos and islands were connected with the mainland, the unique Aral type shore disappeared. Since 1989 the Aral Sea has been split in two separate water bodies: Great Sea and Small Sea connected by a narrow canal which is demonstrated in the satellite data-based map.

The experience in the Aral Sea and other reservoir surface monitoring gained by the Russian specialists within the last years as well as the techniques and technologies developed for value-added processing of satellite data may serve as the basis for studying other ecologically problem water bodies.

Operative space monitoring of water bodies can be performed using the data from the Russian satellite systems that are both operative and scheduled for launch in the coming years.

Presently to study the variations in shoreline of inland reservoirs uses the data from the operative Russian RESURS-DK spacecraft that provides multiband optical imagery with 2-3m resolution and about 40km coverage. This data allow for coastal infrastructure condition to be defined more exactly and marine pollution in the coastal zone to be studied.

In 2009 the Russian METEOR-M1 spacecraft equipped with KMSS multiband instrument of 60m and 120m in spatial resolution and 960km in coverage is scheduled for launch. The imagery from the spacecraft will enable a number of monitoring tasks including water surface estimation, polluted water surface assessment, etc. In addition to optical instruments the METEOR-M1 will be installed with radar equipment to provide imaging within the coverage of about 400km with the 1-2km resolution that will enable imaging of water bodies regardless of cloud and sunlight conditions.

Thus in 2009 there may be established a system for operational monitoring of water bodies by means of the METEOR-M1 spacecraft with a thorough research of coastal zone carried out by means of the RESURS-DK1 spacecraft.

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