Studies to evaluate the spatial–temporal distribution of
the Altai catastrophic flood were conducted in southwestern
Siberia, in the Ob River basin, covering the area from the Altai
foothills to the Novosibirsk Reservoir. Based on meteorological
data,
the period from May 12 to June 16 was selected. In May
13 to 28, a heavy rainfall took place, which caused serious
flooding, leading to floodplain inundation.
To assess the flood dynamics, we used SMOS images with
processing level of L1c , allowing the evaluation of spatial
distribution of brightness temperature TB. The uncertainty of
TB ranged from ±3 K at the center and up to ±6 K at
the edges of a swath width of ∼890 km wide. The satellite
observations were made approximately at 7 A.M. local time by
means of MIRAS in horizontal and vertical polarization mode
at probing angles of 0◦−55◦ and at a frequency of 1.41 GHz.
The radiometer’s resolution varies from 35–50 km and is 45
km at the probing angle of 42.5◦.
SMOS data (L1c) are represented on a discrete geodesic grid
DGG ISEA 4H9 .
observation date and time.
MODIS algorithms for temperature retrieval are based on
the results of passive scanning of upwelling radiation with a
wavelength of 10–12 μm.
Based on the ground measurements, it was found that, during
the morning flight of SMOS over the site, the temperature
gradient in the 0–10-cm layer was less than 0.5 K/cm. For
wetland soils and open areas of water, the thickness of the skin
layer does not exceed a few centimeters. In these conditions,
the difference between the temperatures in the skin layer and
on the surface is not higher than 0.5 K, i.e., it is within the
measurement error.
The emissivity of the underlying surface was estimated from
the brightness (TBH) and thermodynamic (TM) temperatures,
determined by MIRAS and MODIS, according to the formula.
During the ground-based experiment, the soil was sampled
to estimate the volumetric moisture (W) using a gravimetricthermostatic
method with a relative error less than 3% by the
formula W = (ρ/ρW)(MW/M), where MW, ρW, M, and ρ
are the mass and density of water and moist soil.