Xiangkun Zhang

A combined L-band synthetic aperture radiometer and fan-beam scatterometer for soil moisture and Ocean salinity measurement

The concept of a new type combined L-band active and passive sensor for soil moisture and ocean salinity measurement has been proposed in this paper. The passive part of this combined system is a one-dimensional synthetic aperture radiometer, while the active part is a digital beam forming scatterometer. Preliminary considerations for space-borne system design and performance evaluation has also been introduced in this paper. A ground-based demonstrator is defined and under development.

System study and development of an L-band 1-D synthetic aperture radiometer for ocean salinity measurement

System study and development of an L-band one-dimensional synthetic aperture radiometer, or microwave interferometric radiometer (MIR), has been introduced in this paper. This radiometer is the passive part of a combined active/passive instrument for space-based ocean salinity observation. Recent progresses on radiometer hardware development and system simulation have been introduced.

MICAP (Microwave imager combined active and passive): A new instrument for Chinese ocean salinity satellite

Sea surface salinity (SSS) plays an important role in global water cycle. In recent years, satellite based remote sensing has proven to be a promising approach for global SSS observation. A new payload concept, named MICAP (microwave imager combined active and passive), has been introduced in this paper. MICAP is a suit of active/passive instrument package, which includes L/C/K band one-dimensional MIR (microwave interferometric radiometer) and L-band DBF (digital beamforming) scatterometer, sharing a parabolic cylinder reflector. MICAP has been selected to be a candidate payload for future Chinese ocean salinity mission. In this paper, the MICAP instrument concept, specification and preliminary system design will be introduced.

Design of phased array microwave scatterometer with digital beam forming technique in active and passive combining observation system for sea surface salinity

Active and passive combining observation microwave instrument combines L band one dimension push-broom synthetic aperture radiometer and L band array mode microwave scatterometer to make accurate measurement for sea surface salinity. In this system, microwave scatterometer provides the information about the sea surface roughness, one of the main sources of error for salinity measurement. Phased array mode is adopted in scatterometer and the array elements are arranged between two elements with the largest baseline of radiometer. The number of array elements is set to 7 and digital beam forming technique is used to get scanning in cross azimuth direction. Then same footprints with radiometer can be obtained. Narrow band chirp signal is used to get range resolution. In this way, accurate backscattering information corresponds to observing area of radiometer can be achieved and then sea surface roughness can be derived. Finally, the error coming from surface roughness can be corrected.

IMI (Interferometric Microwave Imager): A L/S/C tri-frequency radiometer for Water Cycle Observation Mission(WCOM)

Water Cycle Observation Mission (WCOM) is an earth science mission proposed and focused on the research of water cycle under global change. With its three dedicated designed main payloads, WCOM can achieve synchronized observation on a group of global water cycle key parameters, including soil moisture, ocean salinity, snow water equivalent, soil freeze-thaw, atmospheric water vapor, precipitation and other associated parameters. One of the three WCOM main payloads names IMI (Interferometric Microwave Imager), which is a newly designed L/S/C tri-frequency radiometer aiming to provide advanced measurement capability on soil moisture and ocean salinity. In this paper, the instrument concept and preliminary system design of WCOM/IMI will be introduced. Recent progresses on the filed experiments of an L-band demonstrator will also be introduced.

Experimental performance analysis of the DBF technique on MICAP scatterometer demonstartor

In this paper, we present the experimental results of a DBF (digital beam forming) scatterometer demonstrator performance on the purpose of development and verification of innovative DBF concepts and advanced operational modes for the future space borne MICAP (microwave imager combined active and passive), Chinas ocean salinity mission. The hardware configuration of the demonstrator is introduced. The ground-based experiments, verifying the DBF function on receiving and transmitting separately are carried out on the open field using the demonstrator. Analysis of the experimental results verifies the validity of the DBF technique on the receiving and transmitting. At last, the problems caused by the unbalance of the amplitude and phase between channels are discussed. The function verification experiment is the very first step towards the future space borne MICAP, and further researches are in progress.

ANALYSIS AND VALIDATION OF SUPER-RESOLUTION MICRO-DEFORMATION MONITORING RADAR

A light micro-deformation monitoring radar based on frequency modulation continuous wave (FMCW) technique is proposed and designed for scenes which are sensitive to micro deformation such as slopes, dams, and high buildings. The miniradar is well suited to measure micro-deformation of buildings or mountains. Meanwhile, interferometric method was used by the radar to obtain high range resolution of the micro-deformation monitoring radar. The radar acquires micro deformation of the target by inversion of phase difference between the transmitted and received waves. To get an accurate micro-deformation measure result, the radar was carefully designed in signal mode and hardware structure. Various experiments are used in the article to verify the radar’s deformation measure ability. The experiments prove that the radar can measure micro deformation accurately and timely. For example, railway bridges’ vibration can be monitored by the radar in real time. In addition, it can be used in structures monitoring, disaster alarming and other regions.

A hierarchical model-based polarimetric SAR image decomposition based on coherency matrix

The nonnegative eigenvalue constraint is a complete way to avoid the negative powers in model-based decomposition approaches. But in nonnegative eigenvalue decomposition (NNED), the volume scattering model is always subtracted prior to the remaining scattering mechanisms. Furthermore, the rank of the remaining coherency matrix is acquiescently assumed equal to two, that is to say, expect for the volume scattering the other scattering is weakly depolarized. However, the remaining scattering maybe strongly depolarized owing to the complexity of ground targets. In some sense, in NNED, we assume that the volume scattering contribution is always dominant. Obviously, this is not applicative for all pixels, and the decomposition should be hierarchical according to the dominant scattering mechanism. So in this paper, for the pixels that volume scattering dominates, the general NNED is adopted. For the pixels that surface or dihedral scattering dominates, a new decomposition framework is developed, in which the dominant scattering mechanism can be automatically obtained according to the alpha angle as well as the three corresponding power coefficients. Particularly, we also present an alternative way to alleviate the negative powers by adaptive fitting between model and data, by which the decomposition will be more accurate and stable than the most existing approaches. The results of the proposed scheme show great improvements using the AIRSAR data set.

Surface scattering and emission models for ocean surface salinity remote sensing

Before the program of new type combined active and passive L-band sensor for ocean salinity measurement embarks upon, the behavior of both brightness temperature and backscattering coefficient with sea surface salinity and roughness is premeditated. It is shown that sea surface brightness temperature is sensitive to salinity, which makes the reconstruction of sea surface salinity by brightness temperature possible. In order to refine the measurement and for better reconstruction, the ”excess” brightness temperature engendered by sea surface roughness need to be eliminated. Through illustrating the dramatic change of backscattering coefficient with roughness, the elimination can be practicable.

PolInSAR airborne principle verification experiment based on Ku-band multifunction radar system

With polarimetric techniques introduced into SAR interferometry, comprehensive information about vertical distribution and 2D distribution of scattering mechanisms with polarimetric characteristics can be achieved. As a result, polarization interferometric synthetic aperture radar can provide more accurate, rich data source for mapping, disaster monitoring, vegetation distribution, resource exploration etc. Ku-band Multifunction radar system built in the CAS key laboratory of microwave remote sensing provides a test bench for principle verification. In the recent airborne experiment, several system functions have been proved on this test bench. Effective data were obtained during experiments. Now, H and V channel data are imaging processed respectively using RD algorithm. From processed results, the polarization information of the target is obvious. Analyze the phase of each image of channel H and V.