Orbital radars are used to monitor the state of the sea ice in the Arctic and Antarctic. The backscattering radar cross section (RCS) is used to determine the type of scattering surface. The power of the reflected signal depends on many factors, so the problem of separating sea ice and sea waves is not always unambiguous. Previous research has shown that microwave Doppler radar installed on aircrafts can be used to determine the boundary of sea ice. The width of the Doppler spectrum for wide or knife-like antenna beam depends on the statistical parameters of the reflecting surface, so sea ice and sea waves are easily separated. However, when installing a Doppler radar on a satellite, the spatial resolution becomes extremely low. In this research, we discuss the possibility of improving the spatial resolution by dividing the antenna footprint into elementary scattering cells. To do this, it is proposed to use the original incoherent synthesis procedure, which allows one to determine the dependence of the RCS on the incidence angle for an elementary scattering cell. Numerical modeling was performed and processing of model data confirmed that sea ice and sea waves are separated. The coefficient of kurtosis was used as a criterion in the algorithm. In addition, for sea waves, it is possible to determine the mean square slopes (mss) of large-scale waves, compared to the electromagnetic wavelength of sea waves along the sounding direction.

Remote sensing methods are widely used to monitor ongoing climate change, and the area of sea ice in the Arctic and Antarctic is used as one of the criteria. The duration of ice cover on inland waters can be used to assess processes within continents. The small size of internal waters does not allow the use of traditional methods that have proven themselves well in marine conditions. This study considers the possibility of using dual-frequency precipitation radar data to detect ice formation and destruction on small inland waters. Due to the features of backscatter at small incidence angles (< 18∘), inland waters with sizes smaller than the radar resolution (5 km) are “visible” in radar images. Using the Volga River as an example, it is shown that water-ice and ice-water transitions can be detected when analyzing radar images, and thus, possible to estimate the duration of ice cover on inland waters.

This study addresses the challenge of understanding sea ice microwave scattering properties by developing a novel method to retrieve scattering indicatrix and angular dependence of backscattering patterns from Global Navigation Satellite System Reflectometry (GNSS-R) data. Sea ice remote sensing in quasi-specular reflection area requires theoretical models validated using experimental data across different frequency bands. However, only limited observations of quasispecular scattering in the L-band exist. We developed an algorithm to convert Doppler spectra from delay-Doppler maps (DDM) obtained by the TDS-1 satellite into scattering indicatrix and then to angular dependence of the sea ice backscattering patterns, using geometric transformations from bistatic sensing geometry. The method was applied to approximately 100 DDM measurements over the Sea of Okhotsk during February–March 2017, where ice concentration remained at 90–100% with temperatures below 0 °C. Results show that L-band (19 cm wavelength) exhibits broader angular dependence compared to Ka-band (8.45 mm) and Ku-band (2.21 cm) measurements from dual-frequency precipitation radar (DPR), contrary to expectations based solely on surface roughness. This anomalous broadening is attributed to volume scattering effects within sea ice, where L-band signals penetrate up to one meter depth compared to millimeter-scale penetration in Ka- and Kufrequency bands. The findings provide new insights into L-band scattering mechanisms and offer a validated approach for improving theoretical models of sea ice microwave interaction.

The paper presents the results of a series of experiments performed in February-March 2023. An X-band radar was installed on the metro bridge across the Oka River in Nizhny Novgorod. The radar worked in the radio altimeter mode and the waveform of the reflected pulse was recorded (the dependence of the power of the reflected signal on time). As a result of processing, the distance to the reflection area on the surface was determined. Dependences of the power of the radar signal reflected by the ice cover on the incidence angle were obtained. The air temperature was recorded synchronously with the measurements. The change in the distance to the area of reflection on the surface was associated with a change in the water level in the Oka River. Dependences of the power of the reflected signal on the angle of incidence were plotted for a radar with a knife-like antenna beam for different days of measurements. Based on empirical data, a formula is obtained for the angular dependence of the power of reflected microwave signal for fresh ice cover.

The height of sea waves is one of the most important characteristics describing the wave climate of the ocean. At the present, the main radar for remote measurement of wave heights is an altimeter. Measurements are performed at the vertical sounding (incidence angle equal to zero). The Brown model was developed to describe the waveform of the reflected impulse at the vertical sounding. There is no theoretical model for the case of oblique sounding. In the Kirchhoff approximation, the theoretical task about waveform of the reflected impulse at oblique sounding was considered. In the result of the investigation, the analytical formula for the waveform of the reflected impulse for oblique sounding at the small incidence angles (< 12◦) for a microwave radar with a narrow antenna beam was obtained. The waveform of the reflected impulse depends on the width of antenna beam, incidence angle, impulse duration, significant wave height (SWH), altitude of the radar, mean square slopes of large-scale, in comparison with radar wavelength, sea waves. It is shown that possibility exist to retrieve SWH using waveform the reflected impulse at the oblique sounding.

The purpose of this study is to analyze the applicability conditions for the significant wave height (SWH) measurement approach based on measuring the cross-correlation function of two signals with similar frequencies reflected by the sea surface in the bistatic problem statement (the transmitting antenna and the receiving antenna are separated in space). When implementing this approach, the modulus of the normalized cross-correlation function for several pairs of signals with different frequency bases will be measured in the experiment. The advantage of this approach over the traditional method for radar altimetry, based on the analysis of the shape of the reflected pulse, is the high accuracy in measuring the SWH for weak waves. In the bistatic formulation of the problem, an important advantage of the approach under study is the possibility of obtaining analytical formulas for solving the direct problem. This paper presents the derivation of a formula for the modulus of the normalized cross-correlation function of reflected signals, which expresses an explicit relationship with the parameters of sea waves and the measurement geometry in the bistatic formulation of the problem. This paper considers the influence on the modulus of the normalized cross-correlation function of the antenna patterns of the transmitting and receiving antennas, the distances to the sea surface, the wave slope variances, the SWH and the frequency base of the transmitted signals. The optimal variants of the measurement scheme are discussed. The results and conclusions obtained can be easily expanded to underwater acoustic sounding.