Madhu Chandra

Assessment of Atmospheric Propagation Effects in SAR Images

TerraSAR-X, the first civil German synthetic aperture radar (SAR) satellite, was successfully launched on June 15, 2007. After 4.5 days, the first processed image was obtained. The overall quality of the image was outstanding; however, suspicious features could be identified which showed precipitation-related signatures. These rain-cell signatures are thoroughly investigated, and the physical background of the related propagation effects is provided. In addition, rain-cell signatures from former missions like SIR-C/X and the Shuttle Radar Topography Mission are provided for comparison. During the commissioning phase of TerraSAR-X, a total of 12 000 scenes were investigated for potential propagation effects, and about 100 scenes revealed atmospheric effects to a visible extent. Some of the particularly interesting events were selected and are discussed in greater detail. An interesting case of data acquisition over New York will be presented, which shows typical rain-cell signatures, and the SAR image will be compared with weather-radar data acquired nearly simultaneously (within the same minute). By comparing the images, it can be clearly seen that reflectivities in the weather-radar image of 50 dBZ may cause visible artifacts in SAR images. Furthermore, in this paper, we discuss the influence of the atmosphere (troposphere) on the external calibration of TerraSAR-X. By acquiring simultaneous weather-radar data over the test site and the SAR acquisition, it was possible to flag affected SAR images and to exclude them from the procedure to derive the absolute calibration constant. Thus, it was possible to decrease the 1 sigma uncertainty of the absolute calibration factor by 0.15 dB.

Measurement and Characterization of Entropy and Degree of Polarization of Weather Radar Targets

To date, few polarimetric weather radars have exhibited the capability to measure full scattering matrices. In contrast, in the synthetic aperture radar (SAR) community, considerable experience has been gained in dealing with complete scattering matrices and their statistical behavior. This paper aims to place weather radar parameters in a wider context in order to exploit more general concepts like target decomposition theorems and polarization basis transformations. Entropy, which is a fully polarimetric variable derived from the Cloude-Pottier decomposition, and the degree of polarization, which is derived from Wolfs coherence matrix, are the subject of this paper. The theoretical analysis carried out in the first part is checked against fully polarimetric data from POLDIRAD, which is the german aerospace center research weather radar. The entropy and the degree of polarization are compared with the copolar correlation coefficient in order to understand whether they can add value to radar meteorological investigations. Because the degree of polarization is available to conventional dual-polarization coherent systems, it is important to assess its potential for operational use.

Fully polarimetric analysis of weather radar signatures

In this work the concept of depolarization response, namely the degree of polarization as a function of transmit polarization state, is investigated. Application examples are shown in the field of radar meteorology, namely for hydrometeor identification with fully polarimetric weather radar signatures. Data are from POLDIRAD, DLR research weather radar.

Comparison of methods for extracting and utilizing radar target characteristic parameters

A comparative analysis of different representations of polarimetric SAR data has been carried out. Each representation is considered in terms of the amount and type of information it provides. The investigation is motivated by the fact that, although a large number of decomposition methods are available, a detailed assessment of their characteristics has been missing in the past and still has to be further elaborated. Moreover, some new methods have been recently presented, derived from fields different from radar polarimetry. The features provided by these methods are worthy of a closer investigation and a direct comparison with methods used until now. This is the case, for example, of the principal component analysis (PCA) adapted to polarimetry by Lüneburg and not yet practically tested. On this background, a series of classification tests have been carried out, comparing the results in terms of their accuracy. This approach allows for a quantitative estimate of the information content of the different polarimetric parameters under consideration.

Investigation of microwave and electrical characteristics of Co–Zr substituted M-type Ba–Sr hexagonal ferrite

Abstract Microwave characteristics of M-type hexagonal ferrite, Ba0.5Sr0.5CoxZrxFe(12-2x)O19 (x = 0.0 to 1.0 in steps of 0.2), have been investigated as a function of frequency and substitution at X-band. The microwave absorption has been investigated using absorber testing device method. The static I-V characteristics have been studied as a function of substitution. The results show maximum microwave absorption at higher substitution. The static current exhibits ohmic behavior from 0 to 3 V and exponential trend from 3 to 4.8 V. The microstructure influences both microwave and electrical properties. The ferrite compositions for different electromagnetic applications are also suggested by measuring the microwave absorbed, transmitted and reflected power.

Overview of modern multi-parameter methods of radar remote sensing in context of disaster management

Recent advances in Radar Remote Sensing cover an impressive list of developments, such as: waveform diversity, polarization diversity, frequency diversity, input-output channel diversity (MIMO), beam-forming and beam tailoring in send-and-receive modes!

Investigation of microwave characteristics of Ca-Co-Ti ferrite for electromagnetic applications

In this investigation, we are reporting microwave characterization of M-type CaCo x Ti x Fe (12−2x) O 19 ferrite for different electromagnetic applications using Absorber Testing Device (ATD) [1] method.

Degree of polarization for weather radars

Future operational weather radars are likely to implement hybrid polarization, an operating mode that involves transmitting 45deg slant polarization and receiving the horizontal and vertical components of the backscattered field. In this work, the degree of polarization at slant send is theoretically considered and experimentally evaluated from fully polarimetric signatures in order to assess its potential for use in next generation operational weather radars.

On the statistical aspects of radar polarimetry

A comparison between the Kennaugh matrix and the covariance matrix formulation of secondorder moment radar polarimetry reveals fundamental relationships between power and variance aspects of bi-static and mono-static radar scattering from randomly distributed targets.

Propagation induced distortion of Wideband Waveform radar signals in dependence of polarisation and frequency

Wideband Waveform radar signals of Bandwidths in excess of 300 MHz are anticipated to play an important role in the emerging systems in radar remote sensing. In telecommunication and remote sensing applications, large-bandwidth signals are required for generating high channel capacity and data-transfer rates. In radar-imaging applications, large bandwidths are required for obtaining higher spatial resolution, for instance. The well-known benefits of wideband signals, however, are available only under the premise that the free-space propagation effects do not distort or impair the amplitude and phase composition of the different frequency components contained in such signals. Indeed, the so-called free-space is, however, often filled with precipitation media, such as rain. Contrary to popular belief, such media are capable of generating dispersion by causing unequal attenuation and phase-shift of the different frequency components present in the wideband signal. In this contribution, we shall report investigations in this regard.