Igor Kozlov

Quad‐polarization SAR features of ocean currents

A methodology is demonstrated to exploit the polarization sensitivity of high-resolution radar measurements to interpret and quantify upper ocean dynamics. This study particularly illustrates the potential of quad-polarization synthetic aperture radar (SAR) measurements. The analysis relies on essential characteristics of the electromagnetic scattering mechanisms and hydrodynamical principles. As the relaxation scale of centimeter-scale ocean surface scatters is typically small, radar signal anomalies associated with surface manifestations of the upper ocean dynamics on spatial scales exceeding 100 m are mostly dominated by nonresonant and nonpolarized scatters. These “scalar” contributions can thus efficiently trace local breaking and near-breaking areas, caused by surface current variations. Using dual copolarized measurements, the polarized Bragg-type radar scattering is isolated by considering the difference (PD) between vertically and horizontally polarized radar signals. The nonpolarized (NP) contribution associated with wave breaking is then deduced, using the measured polarization ratio (PR) between polarized signals. Considering SAR scenes depicting various surface manifestations of the upper ocean dynamics (internal waves, mesoscale surface current features, and SST front), the proposed methodology and set of decompositions (PD, PR, and NP) efficiently enable the discrimination between surface manifestation of upper ocean dynamics and wind field variability. Applied to quad-polarized SAR images, such decompositions further provide unique opportunities to more directly assess the cross-polarized (CP for HV or VH) signal sensitivity to surface roughness changes. As demonstrated, such an analysis unambiguously demonstrates and quantitatively evaluates the relative impact of breakers on cross-polarized signals under low to moderate wind conditions.

Internal Solitary Waves in the Laptev Sea: First Results of Spaceborne SAR Observations

The first results of internal solitary wave (ISW) observations over the ice-free Laptev Sea derived from 354 ENVISAT Advanced Synthetic Aperture Radar (ASAR) images acquired in May–October 2011 are reported. Analysis of the data reveals the key regions of ISW distribution that are primarily found over the outer shelf/slope regions poleward the M2 critical latitude. Most of the ISWs are observed in regions where enhanced tide-induced vertical mixing and heat fluxes have been previously reported. This suggests that spaceborne SAR observations may serve as a tool to infer local mixing hot spots over the ice-free Arctic Ocean.

SAR observations of internal waves in the Russian Arctic seas

In this work taking the advantage of high resolution spaceborne synthetic aperture radar (SAR) measurements we present first preliminary results of short-period internal waves (IW) observations in the Barents, Kara and White seas based on ENVISAT ASAR data for summer-autumn months in 2007-2011. Altogether more than 2000 IW packets were identified in about 1400 SAR images. Detailed maps of internal waves occurrences in the three Arctic seas have helped to identify main sites of regular IW generation.

Monitoring short-period internal waves in the White Sea

Widespread short-period internal wave (SPIW) activity in the White Sea has been revealed for the first time based on long-term (2009–2013) monitoring performed using satellite and in situ observations, and the statistical characteristics of these waves have been obtained. Two main regions where short-period waves constantly exist have been identified: the shelf area near the frontal zone at the boundary between the Basin and the Gorlo Strait and the shallow shelf area where the depths are about 30–50 m near Solovetskie Islands. Intense internal waves (IIWs), which are substantially nonlinear and are related to specific phases of a barotropic tide, are regularly observed near frontal zones. The wave height can reach half the sea depth and the wave periods vary from 7 to 18 min.

Quad-polarized SAR measurements of ocean currents in C- and L-bands

In this study we exploit the polarization sensitivity of high-resolution SAR measurements in C- and L-bands using a methodology suggested in [1, 2] to study the physics of radar imaging of upper ocean dynamics. Using samples of RADARSAT-2, ALOS PALSAR and ALOS-2 PALSAR-2 quad-polarization ocean SAR scenes, we decompose dual co-polarized (VV and HH) radar data into polarization difference (PD) and non-polarized (NP) components. Following [1, 2] these quantities provide means to distinguish Bragg scattering and non-polarized radar returns related to the quasi-specular reflection from breaking waves and from slopes of “regular” large-scale waves, and assess their relative role in the formation of surface current signatures in C- and L-band SAR ocean images. While C-band SAR features of ocean currents are fully dominated by non-resonant and non-polarized radar scattering from breaking waves, their manifestation in L-band SAR images are formed by Bragg waves, wave breaking and large-scale “regular” waves modulations by the currents.

Remote sensing of shortwave solar radiation and near-surface air temperature changes in the south-eastern baltic

The main aim of this work is to determine shortwave solar radiation and near surface air temperatures changes in the south-eastern (SE) Baltic region during 2000-2013 using satellite data and remote sensing methods. The amount of solar radiation that reaches the Earth surface (both land and sea surfaces) and its atmosphere defines the local temperatures, meteorological conditions and may indicate climate change processes in the environment systems. Therefore solar radiation reaching the Earth is the main energy source governing the surface temperature dynamics both on the land and in the ocean. While the grid of meteorological stations measuring the solar radiation is rather sparse, satellite remote sensing data can be effectively used instead. However, the latter should also be treated carefully taking into account signal absorption, atmospheric clarity, could coverage, etc. In this work Terra and Aqua, MODIS and AIRS data of 15 x 15 km resolution was used to evaluate the incoming shortwave solar radiation and near-surface air temperature in the SE Baltic. Space-derived estimates were then compared with regular observations taken at the meteorological stations. The results of the work fairly demonstrate how CM SAF satellite data could be applied for the coastal climate zone indication, breeze dynamics research and cartography of the whole Baltic region.

Space-derived parameters of coastal upwelling in the SE Baltic Sea

In this work we present a basic statistics of coastal upwelling parameters inferred from satellite infrared (IR) Terra/Aqua MODIS sea surface temperature (SST) maps acquired over the South-Eastern (SE) Baltic Sea between 2000 and 2013. The maximum observed SST gradients across the front were up to 1.6 °C/km, temperature drop up to 14°C with total upwelling-affected area up to 16000 km2. The observed horizontal scale of the upwelling is about 100-400 km along the coast, and 10-20 km (max 70-80 km) cross-shore. The duration of the upwelling in this part of the sea is from several days up to several weeks. It is found that intensive coastal upwelling in the SE Baltic may lead up to 40-km long intrusion of relatively cold and saline sea water into the Curonian Lagoon forming very pronounced property gradients there and affecting nearly a half of the Lithuanian part of the lagoon.

Advancing coastal upwelling observations with use of SAR data: Case study from SE Baltic

Nowadays exploitation of satellite data, mostly infrared and visible, became a regular practice for upwelling detection and analysis. At the same time these types of satellite data strongly depend on sun illumination conditions and cloud cover, with the latter being very limiting factor specifically for the Baltic Sea. In this case SAR (Synthetic Aperture Radar) imagery not affected by clouds and with high spatial resolution can significantly contribute to upwelling observations. The aims of this study are to show how SAR complements both in situ and satellite optical data, and to examine general SAR limitations to observe sea surface temperature (SST) fronts associated with coastal upwelling.