Alexey Nekrasov

Doppler Navigation System with a Non-Stabilized Antenna as a Sea-Surface Wind Sensor

We propose a concept of the utilization of an aircraft Doppler Navigation System (DNS) as a sea-surface wind sensor complementary to its normal functionality. The DNS with an antenna, which is non-stabilized physically to the local horizontal with x-configured beams, is considered. We consider the wind measurements by the DNS configured in the multi-beam scatterometer mode for a rectilinear flight scenario. The system feasibility and the efficiency of the proposed wind algorithm retrieval are supported by computer simulations. Finally, the associated limitations of the proposed approach are considered.

Sea Wind Measurement by Doppler Navigation System with X-Configured Beams in Rectilinear Flight

We suggest a conceptual approach to the measurement of the near-surface wind vector over water using a Doppler navigation system, in addition to its standard navigation capabilities. We consider a Doppler navigation system with a track-stabilized antenna and x-configuration of its beams. For the measurement of the sea-surface wind, the system operates in the multi-beam scatterometer mode in rectilinear flight. The proposed conceptual design has been validated, and its accuracy for the wind vector measurement has been estimated using Monte Carlo computational simulations.

Airborne weather radar concept for measuring water surface backscattering signature and sea wind at circular flight

KLJUČNE RIJEČI vjetar na moru refleksija s morske površine meteoradar u zrakoplovu algoritam Alexey Nekrasov Saint Petersburg Electrotechnical University, Saint Petersburg, Russia Southern Federal University, Taganrog, Russia Hamburg University of Technology, Hamburg, Germany e-mail: alexei-nekrassov@mail.ru Vladimir Veremyev Saint Petersburg Electrotechnical University Saint Petersburg, Russia e-mail: ver_vi@mail.ru

A concept for measuring the water-surface backscattering signature by airborne weather radar

A concept for measuring the water-surface backscattering signature using the airborne weather radar, in addition to its standard meteorological and navigation applications, is discussed. The airborne weather radar operates in the ground-mapping mode in the range of high to medium incidence angles as a scatterometer. A case of two-stage rectilinear track flight measurement with a 180° aircraft turn between the stages is considered. Some limitations and recommendations to perform the measurement are presented.

Optimization of Airborne Antenna Geometry for Ocean Surface Scatterometric Measurements

We consider different antenna configurations, ranging from simple X-configuration to multi-beam star geometries, for airborne scatterometric measurements of the wind vector near the ocean surface. For all geometries, track-stabilized antenna configurations, as well as horizontal transmitter and receiver polarizations, are considered. The wind vector retrieval algorithm is generalized here for an arbitrary star geometry antenna configuration and tested using the Ku-Band geophysical model function. Using Monte Carlo simulations for the fixed total measurement time, we show explicitly that the relative wind speed estimation accuracy barely depends on the chosen antenna geometry, while the maximum wind direction retrieval error reduces moderately with increasing angular resolution, although at the cost of increased retrieval algorithm computational complexity, thus, limiting online analysis options with onboard equipment. Remarkably, the simplest X-configuration, while the simplest in terms of hardware implementation and computational time, appears an outlier, yielding considerably higher maximum retrieval errors when compared to all other configurations. We believe that our results are useful for the optimization of both hardware and software design for modern airborne scatterometric measurement systems based on tunable antenna arrays especially, those requiring online data processing.

On off-nadir wind retrieval over the sea surface using APR-2 or similar radar geometry

ABSTRACT In some cases, nadiral wind retrieval algorithms are not applicable for wind measurements due to the specificity of a radar instrument measuring geometry or its mounting on aircraft, and so off-nadir backscattering measurements can only be performed. In this paper, a method for off-nadir wind retrieval over the sea based on the sea-surface backscattering measurements with the Airborne Precipitation Radar-2 or similar radar measuring geometry has been proposed. The study is based on a theory of the quasi-specular microwave backscattering from the sea surface. An anisotropic water surface approach is considered. The wind vector is retrieved from the system of equations for measured normalized radar cross sections (NRCS) by using the relationships between the speed of the sea-surface wind and the standard deviations of the sea-surface slopes along the up- and cross-wind directions. A wind vector recovery with the cross-track scanning measurement geometry has been simulated. The maximum errors of the wind speed and direction estimations are within typical errors of wind measurements by a scatterometer. A maximum altitude of the method applicability for this geometry has been defined. Recommendations to perform the measurements have been described in detail.

Near-Nadir Wind Estimation Over Water with Airborne Precipitation Radar

Remote sensing of sea surface wind by means of a radar altimeter is based on specular returns from water surface. A wind retrieval algorithm deriving the wind speed from the NRCS at nadir incidence angle is used in that case.

Water-Surface Wind Retrieval Using Airborne Radar Altimeter

Radar altimeters are frequently used by aircraft. The primary function of the ARA is to provide terrain clearance or altitude with respect to the ground level directly beneath the airplane or helicopter.

Water Surface Backscattering and Wind Retrieval

Many researchers have been investigating the microwave backscattering signatures of water surface and solving the problem of remote measuring of wind speed and direction over water (Bentamy et al. 2012; Carswell et al. 1994; Chelton and McCabe 1985; Feindt et al. 1986; Giovanangeli et al. 1991; Hildebrand 1994; Long 2001; Masuko et al. 1986; Melnik 1980; Moore and Fung 1979; Nielsen and Long 2009; Plant 2003; Ward et al. 2008; Wismann 1989). However, the mechanics of interactions between water surfaces and microwaves has not been well studied in detail.

FM-CW Demonstrator System as an Instrument for Measuring Sea Surface Backscattering Signature and Wind

In the field of airborne earth observation, there is growing interest in small, cost effective radar systems. Such radar systems should consume little power and be small enough to be mounted on light, possibly even unmanned, aircraft. FM-CW radar systems are generally compact, relatively cheap, and they consume little power. Consequently, FM-CW radar technology seems to be of interest to civil airborne earth observation, particularly in combination with high resolution SAR techniques.