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ISSN 2070-7401 (Print), ISSN 2411-0280 (Online)
Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa
CURRENT PROBLEMS IN REMOTE SENSING OF THE EARTH FROM SPACE

  

Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2026. Т. 23. № 3. С. 291-303

Changes in the area of the Caspian Sea and the Kara-Bogaz-Gol Bay under conditions of water level decline (1993–2025)

A.V. Bocharov 1, 2, 3 , A.G. Kostianoy 2, 4, 5 , S.A. Lebedev 4, 6, 7 , S.I. Bidenko 8 
1 Tver State University, Tver, Russia
2 Shirshov Institute of Oceanology RAS, Moscow, Russia
3 Water Problems Institute RAS, Moscow, Russia
4 Maykop State Technological University, Maykop, Russia
5 Moscow Witte University, Moscow, Russia
6 Geophysical Center RAS, Moscow, Russia
7 National Research University of Electronic Technology, Zelenograd, Moscow, Russia
8 JSC "SPA "Impuls", Saint Petersburg, Russia
Accepted: 17.03.2026
DOI: 10.21046/2070-7401-2026-23-3-291-303
The aim of the study is to estimate the area of the Caspian Sea using remote sensing data and to construct hypsometric curves of water surface of the Caspian Sea and the Kara-Bogaz-Gol Bay separately, showing how the surface area varies depending on water level. High resolution (30 m) optical and thermal data from Landsat-5, -7, and -8 satellites, obtained using the Google Earth Engine platform, were used to estimate the area. To minimize the influence of cloud cover, mosaics of images from three summer months of each year were used. The boundaries of the Caspian Sea and the Kara-Bogaz-Gol Bay were delineated using a method based on the separation of near-infrared channel pixels by a threshold value. The study examines the period from 1993 to 2025, which is characterized by a sea level drop of 2,6 m since 1995. The information on Caspian Sea and Kara-Bogaz-Gol Bay levels was obtained from the HYDROWEB (Theia Hydroweb Operational Altimetry Lake Water Level and Storage, LEGOS, France) altimetry database, which was adjusted by 0.43 m to bring it closer to the Baltic Height System. The study proposes regression equations for calculating the area of the Caspian Sea and the Kara-Bogaz-Gol Bay from their water levels. All resulting regression equations are characterized by a very strong statistical relationship between water level and area of the reservoirs, with determination coefficients of 0.95–0.99. The authors recommend using the regression equations to calculate the area of the Caspian Sea at sea levels between –26 and –29 m and for the Kara-Bogaz-Gol Bay at water levels between –27.1 and –31 m.
Keywords: Caspian Sea, Kara-Bogaz-Gol, hypsometric curves, Landsat, satellite altimetry, sea area, sea level
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