Huaze Gong

SAR data for subsurface saline lacustrine deposits detection and primary interpretation on the evolution of the vanished Lop Nur Lake

Lop Nur was a huge lake located at the eastern end of the Tarim Basin, northwest of China, which dried up prior to 1970. Using synthetic aperture radar (SAR), which has the advantage of penetration capability and sensitivity to moist saline materials, the subsurface lacustrine deposits were revealed. SAR also delineated the partially buried shorelines and detailed a complete picture of Lop Nur Lake that led to three important scientific findings. Based on the interpretation of the scattering mechanism of polarimetric and multiple frequency SAR data, field investigation, and sample analysis, it was found that the total area of the vanished Lop Nur Lake was more than 10 000 km2, which is much larger than earlier reports. The relatively young West Lake was superposed on top of the lacustrine deposits of East Lake, making the well known “Ear” feature of Lop Nur, so the western part of the shoreline was buried and not visible on optical remote sensing images. Therefore the Lop Nur Lake actually has near circular, closed shorelines. The drying-up process of East Lop Nur Lake went through six phases according to the shorelines interpreted from multiple SAR data. The shrinking phases of Lop Nur Lake indicate the climate changes between wet and dry environmental conditions.

Scattering Mechanisms for the "Ear" Feature of Lop Nur Lake Basin

Lop Nur is a famous dry lake in the arid region of China. It was an important section of the ancient “Silk Road”, famous in history as the prosperous communication channel between Eastern and Western cultures. At present, there is no surface water in Lop Nur Lake basin, and on SAR (Synthetic Aperture Radar) images, it looks like an “Ear”. The objective of this paper is to interpret the Lop Nur phenomenon from the perspective of scattering mechanisms. Based on field investigation and analysis of sample properties, a two-layer scattering structure is proposed with detailed explanations of scattering mechanisms. In view of the rough surface, the MIEM (Modified Integral Equation Model) was introduced to represent air-surface scattering in Lop Nur. Then, a two-layer scattering model was developed which can describe surface scattering contribution. Using polarimetric decomposition, validations were carried out, and the RMSE (root mean square error) values for the HH and VV polarizations were found to be 1.67 dB and 1.06 dB, respectively. Furthermore, according to model parametric analysis, surface roughness was identified as an apparent reason for the “Ear” feature. In addition, the polarimetric decomposition result also showed that the volume scattering part had rich texture information and could portray the “Ear” feature exactly compared with the other two parts. It is maintained that subsurface properties, mainly generating volume scattering, can determine the surface roughness under the certain climate conditions, according to geomorphological dynamics, which can help to develop an inversion technology for Lop Nur.

Subsurface microwave remote sensing and scattering modelling on hyper-saline soil: Example of Lop Nur

Subsurface microwave remote sensing is a direction of Synthetic Aperture Radar (SAR) research. With the penetration capability, SAR is capable of detecting the subsurface targets and materials, especially in arid environment. Lop Nur Lake is located at the east of Tarim Basin in Xinjiang province of China, which is described as “dry core” of the world, and it can provide conditions for SAR penetration. This paper presents preliminary analysis about Lop Nur, and gives out an abstract subsurface structure about it. Then, the major scattering processes are concluded and a two-layer scattering model is developed. Based on parameters of soil samples, some rules about Lop Nur evolution will be figured out. With Genetic Algorithm (GA), an inversion procedure is constructed. All the attempts are viewed as the basis of future comprehensive interpretation about Lop Nur phenomenon.

Modeling and Mapping Soil Moisture of Plateau Pasture Using RADARSAT-2 Imagery

Accurate soil moisture retrieval of a large area in high resolution is significant for plateau pasture. The object of this paper is to investigate the estimation of volumetric soil moisture in vegetated areas of plateau pasture using fully polarimetric C-band RADARSAT-2 SAR (Synthetic Aperture Radar) images. Based on the water cloud model, Chen model, and Dubois model, we proposed two developed algorithms for soil moisture retrieval and validated their performance using experimental data. We eliminated the effect of vegetation cover by using the water cloud model and minimized the effect of soil surface roughness by solving the Dubois equations. Two experimental campaigns were conducted in the Qinghai Lake watershed, northeastern Tibetan Plateau in September 2012 and May 2013, respectively, with simultaneous satellite overpass. Compared with the developed Chen model, the predicted soil moisture given by the developed Dubois model agreed better with field measurements in terms of accuracy and stability. The RMSE, R2, and RPD value of the developed Dubois model were (5.4, 0.8, 1.6) and (3.05, 0.78, 1.74) for the two experiments, respectively. Validation results indicated that the developed Dubois model, needing a minimum of prior information, satisfied the requirement for soil moisture inversion in the study region.

Applications of polarimetric decomposition technology in a dried up lake evolution

This paper presents fundamental reason to Lop Nur “Ear” feature based on polarimetric decomposition technology. Lop Nur is located at the east Tarim Basin in China, and in history, all the major rivers running in Tarim Basin converged to this lowest place. Lop Nur belongs to arid region, and satisfies penetration conditions for SAR signals. Through comparison between decomposed volume scattering contribution and sub-surface salinity, it is found that subsurface properties (such as salinity) is the fundamental reason to “Ear” feature. And dynamic mechanism of geomorphology builds the relationship between surface and subsurface evolution processes, and indirectly unifies previous points on the reasons to formation of Lop Nur “Ear”. Polarimetric technology is anticipated to be used to retrieve more information and to help extend applications in environment of arid region.

Improved model for dielectric behavior of moist saline soil

This paper introduces a new amendment dielectric model in the microwave band concerning the principle of soil science which can also give the information about soil texture and variety of soluble salt ions, and points out some errors of original model at the same time. The new model is confirmed suitable for saline soil with different levels of moisture and salinity soil samples prepared in lab. Based on the research on the dielectric properties of saline and alkali soils, this paper also brings forward the feasibility of separating them. Contrasts to the classic dielectric models of soil, all the parameters of the improved model have their physical meanings, and the procedures avoid neglecting principle of soil science and optimization blindly. So the parameters can give us more information about moist saline soil. This study sums up dielectric properties of moist soil, and adds salt-affected factor. Thus we can describe dielectric behavior of moist saline soil more precisely. In further research it pays attention to the relationship between dielectric properties and backscattering coefficients or polarimetric information extracted from radar image.

Salt Content Distribution and Paleoclimatic Significance of the Lop Nur “Ear” Feature: Results from Analysis of EO-1 Hyperion Imagery

Lop Nur, a playa lake located on the eastern margin of Tarim Basin in northwestern China, is famous for the “Ear” feature of its salt crust, which appears in remote-sensing images. In this study, partial least squares (PLS) regression was used to estimated Lop Nur playa salt-crust properties, including total salt, Ca2+, Mg2+, Na+, Si2+, and Fe2+ using laboratory hyperspectral data. PLS results for laboratory-measured spectra were compared with those for resampled laboratory spectra with the same spectral resolution as Hyperion using the coefficient of determination (R2) and the ratio of standard deviation of sample chemical concentration to root mean squared error (RPD). Based on R2 and RPD, the results suggest that PLS can predict Ca2+ using Hyperion reflectance spectra. The Ca2+ distribution was compared to the “Ear area” shown in a Landsat Thematic Mapper (TM) 5 image. The mean value of reflectance from visible bands for a 14 km transversal profile to the “Ear area” rings was extracted with the TM 5 image. The reflectance was used to build a correlation with Ca2+ content estimated with PLS using Hyperion. Results show that the correlation between Ca2+ content and reflectance is in accordance with the evolution of the salt lake. Ca2+ content variation was consistent with salt deposition. Some areas show a negative correlation between Ca2+ content and reflectance, indicating that there could have been a small-scale temporary runoff event under an arid environmental background. Further work is needed to determine whether these areas of small-scale runoff are due to natural (climate events) or human factors (upstream channel changes).

Multi-source SAR remote sensing data for emergency monitoring to Wenchuan Earthquake damage assessment

Synthetic Aperture Radar (SAR) has significant advantages in disaster monitoring that are all weather, independent of illumination imaging capabilities and strong stereoscopic sense. SAR technology played irreplaceable role in rapid response to Wenchuan Earthquake monitoring and damage assessment. With multi-source and multi-temporal high resolution SAR images, we conduct rapid, systematic and seriate observations regarding to town damage and secondary disaster in Wenchuan Earthquake area. And based on special SAR image characteristics of building damage conditions, distributions and scopes of landslides and dammed lakes, we carried out rapid quantitative evaluation and built corresponding interpretation symbols. The detection reports and achievements are presented to related apartments of country and rescue teams, supplying full and accurate scientific basis about emergency service and disaster relief.

Detection subsurface hyper-saline soil in Lop Nur using full-polarimetric SAR data

This paper presents the research results about Lop Nur using full-polarimetric technology. Lop Nur Lake is one of the driest places in the world and finally lost its last drop of water in 1972. It is well known for its “Earth Ear” feature in optical remote sensing images. Likewise, “Ear” feature is shown in Synthetic Aperture Radar (SAR) images, and even larger because of penetration effect. With the penetration capability SAR is capable of detecting the subsurface targets and materials, especially in arid environment. As for SAR images, both C-band and L-band, there are two key features about Lop Nur area. One is the whole Lop Nur area is high-bright that means the backscattering is much stronger than other sites, such as Gobi, desert and so on. The other feature is the “Ear” pattern formation. polarimetric analysis about these two questions will be conducted based on past research results and field investigations.

Extension of the Monte Carlo Coherent Microwave Scattering Model to Full Stage of Rice

The ear layer, which is a component of rice, is crucial to rice monitoring and yield estimation. By adding in the ear layer, we have extended the original coherent microwave scattering model, which is based on both the first-order solution of the radiation transfer equation and Monte Carlo numerical simulation methods, to full stage of rice. The detailed scene generation and the geometrical description of rice elements are presented. The propagation path of scattering in rice canopy is reduced. Two approximation methods are used to fit the curving ear by straight cylinders. Ground truth measurements of rice fields in heading stage, including the curvature of ear, were acquired extensively at Jinhu, Jiangsu in eastern China. Measured parameters are used in the new extended model to calculate the C-band backscattering coefficients of rice field. The simulation results are used for comparison with the backscattering coefficients extracted from RADARSAT-2 images to test the validity of the coherent scattering model with the mean absolute error reaching <; 3.3 dB in the copolarization mode. Theoretical analysis reveals that the ear morphology can largely affect the backscattering behavior of the rice field.