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Development and initial testing of a regional stratified algorithm for water turbidity determination in the Sulak River mouth area

P.D. Zhadanova¹

¹ Space Research Institute RAS, Moscow, Russia

Accepted: 15.10.2026
DOI: 10.21046/2070-7401-2026-23-5-170-182

The results of the development and initial testing of a regional algorithm for water turbidity retrieval in the Sulak River mouth area using data from the Operational Land Imager (OLI) on Landsat-8, Operational Land Imager-2 (OLI-2) on Landsat-9, and Multispectral Instrument (MSI) on Sentinel-2 are presented. The regional approach is motivated by the high variability of river discharge and the differing performance of standard algorithms under different optical conditions. A total of 155 quasi-synchronous satellite and in situ observations from eight scenes were used. Training and test datasets were separated at the scene level. Regional recalibration of the Nechad and Dogliotti models did not improve their performance on the test data. A logarithmic model for three turbidity regimes was then developed. Accuracy was assessed using the root mean square error (RMSE), mean absolute error (MAE), mean signed error (Bias), and coefficient of determination (R²). For autonomous application, the regime was determined based on a spectral indicator calculated as the natural logarithm of the water reflectance in the near-infrared, with smooth blending of local models. The final model showed a high correlation with field measurements, outperforming Dogliotti on all four metrics considered, and Nechad on RMSE, MAE, and R², outperforming Dogliotti in all four metrics and Nechad in RMSE, MAE, and R². Spatial application of the algorithm produced no visible discontinuities between regimes and preserved the structure of the river plume. Further independent measurements, especially in the high-turbidity range, are required for a final assessment of the algorithm’s transferability.

Keywords: water turbidity, in situ measurements, regional algorithm, stratified model, ACOLITE, Landsat-8/9, Sentinel-2, Caspian Sea, Sulak River

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References:

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