Wenji Zhao

'Maximal effective baseline' for conventional SAR interferometry

As is well known, perpendicular baselines coming close to the critical baseline will most likely give poor results or even not give any results in conventional SAR interferometry. In the present paper, we put forward a new concept named ‘maximal effective baseline’ for conventional SAR interferometry, which is intrinsically different from the concept of ‘critical baseline’. It is defined as ‘an upper limit of perpendicular baseline for specific SAR system, and it is impossible to obtain necessary coherence to implement conventional SAR interferometry as long as the perpendicular baseline of SAR image pair is beyond this upper limit’. Then, the theoretical approach to determine the maximal effective baseline for conventional SAR interferometry is presented, and the concrete values of maximal effective baselines for ERS1/2 and JERS are yielded by analysing various decorrelation sources. Further more, some InSAR experiments have been made to confirm the results. The ‘maximal effective baseline’ for conventional SAR interferometry is of practical significance in improving the working efficiency of conventional SAR interferometry.

Ecological environment effect analysis of Wetland change in Beijing region using GIS and RS

By utilizing TM/ETM+ remote sensing images from 1984 to 2004 as the major data sources, combining with the field survey to get the rule of dynamic process of Beijing wetland ecosystem, this paper systematic analyzed the hydrology, soil, plant condition of the typical wetland area- Widgeon Lake Wetland Natural Reserve in Beijing. And the results are as follows: In recent years, wetland areas were sharply reduced by half. The negative ecological effects around wetland areas have a close relationship with the deterioration of wetland resources. Salinized area had increased every year and reached to a head in 2004, which accounted for about 21.79 square kilometers. The serious and medium level salinity areas were in the majority in region. Due to the soil salinization, the marsh vegetation species changed to the mesophytic, xeromorphic and salt tolerable ones. Along with the continuously shrinking of water area, wetland dominated the low coverage. The area of medium to high and high coverage in 2004 reduced 71.09 percent and 99.26 percent respectively compared with those in 1998. The regional vegetation cover had shown the degradation trend. Accordingly the soil conservation function of vegetation weakened and soil fertility declined. The cold-humid effect of wetland had been impaired for the breakage of wetland environment in recent years, which led to the drying and warming tendency of regional microclimate. The phenomenon of the decrease amount of regional daily evapotranspiration proved that the climate was drying and warming. The serious disequilibrium between source and sink landscape in every sub-watershed of wetland was an important factor to cause non-point source pollution. The nonpoint source pollution in upper reaches of wetland had caused the high eutrophic water in recent years. From the field water quality monitor we could find the main contaminations were total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD) and fluorid (F). Water quality has reduced up to IV or V grade. The wetland landscape shape fragmentation indexes were all over 0.99 from 1998 to 2002, which showed the impacts of human disturbance on landscape was intensive, the wetland landscape had suffered a serious destruction and the ecology was instability. Based on the above analysis, the regional ecological negative effects were closely connected with the decrease of wetland resources. We should bring forward corresponding effective protection and utilization measures and give the scientific basis for the restoration of wetland resources.

Subpixel urban area thermal pattern analysis using ASTER and SPOT-5

Although lacking fine resolution as airborne sensors, satellite thermal remote sensors are important to urban thermal pattern researches. With the help of downscaling methods and spectral mixing analysis, medium spatial resolution thermal infrared satellite data can retrieve subpixel thermal characteristics by integrating higher resolution and multi-spectral data. Combining SPOT-5 and ASTER is a practical downscaling method among them. Several different means in such procedure are compared and result is acceptable.

An integrated soft and hard classification approach for evaluating urban expansion from multisource remote sensing data: a case study of the Beijing–Tianjin–Tangshan metropolitan region, China

ABSTRACT Integrating soft and hard classification to monitor urban expansion can effectively provide comprehensive urban growth information to urban planners. In this study, both the impervious surface coverage (as a soft classification result) and land cover (as a hard classification result) in the Beijing–Tianjin–Tangshan metropolitan region (BTTMR), China, were extracted from multisource remote sensing data from 1990 to 2015. Then, we evaluated urban expansion based on centre migration, standard deviation ellipse, and spatial autocorrelation metrics. Furthermore, the differences between the soft and hard classification results were analysed at the landscape scale. The results showed that (1) the impervious surface area increased considerably over the past 25 years. Notably, the areas of urban built-up land and industrial production land increased rapidly, while those of ecological land and agricultural production land seriously decreased. (2) The distribution of impervious surfaces was closely related to the regional economic development plan of ‘One Axis, Two Wing, and Multi-Node’ in the BTTMR. (3) The contributions of different land use types to impervious surface growth ranked from high to low as follows: urban built-up land, rural residential land, industrial production land, agricultural production land, and ecological land. (4) The landscape metrics varied considerably based on the hard and soft classification results and were sensitive to different factors.

A CHMT model based DE-speckling method for SAR image

A coarse-classification based tying method for the Contourlet-domain Hidden Markov Tree model (CHMT) solution algorithm is proposed to speed up the parameters estimation; and a general SAR image filtering framework, to which any kind of shift-variant transform can be applied, is generated by applying together with the LOG Transform, mean rectification and cycle-spinning, etc. The proposed coarse classification based tying method for CHMT is applied to de-speckle the SAR image in the general framework, and the result is compared with those of some commonly-used filters. The visual effects and the statistical parameters indicate that the coarse-classification based tying method for CHMT is much faster than the other tying methods, and the CHMT based de-speckle method can achieve better result than some commonly-used filters.

Appraisal of Beijing Wetlands Water Purification Value

Wetland is a kind of land resources and also a kind of ecological environment, it play more important role in people daily lives. Wetland has the vital role in the ecosystem such as storage of water, transformation of nutrients, especially its water purification function, which has important economy and ecological value. The wetlands water purifies mainly aims at nitrogen and phosphorus which causes water body eutrophication pollutant, the wetlands together with the soil, the microorganism and vegetation removes the pollutant. This research mainly aims at the economic value of Beijing wetlands water quality to carry on the appraisal, according to Beijing wetland division standard, through to the different types of wetlands field survey, finally identifying the type of water purification is: The rivers wetlands, the water reserve wetlands, the marsh wetlands, and select 5 typical wetlands areas to take the water quality sampling area, finally applies the type the value of water purification unit area applied to the corresponding types of wetlands, thus obtains Beijing wetlands water purification value.

Strategy of Water Resources Protection for Guishui River, China

In the Yanqing area, Beijing, China agriculture water use and soil erosion are significantly serious due to large-scale agricultural irrigation; It has been the most prominent issue of agricultural irrigation for water resources protection, mainly because irrigation water use utilization efficiency is very low. The key issue of water-saving agriculture is to improve the utilization of irrigation. In this research, Guishui River in Yanqing County, Beijing with water eco-system protection function has been selected as the study location which experiences period of drought and wetness annually. Based on the hydrology methodology and support of the field surveys and continuous observation means for hydrology environmental elements, combined with experiments of vadose zone water transport mechanism, integrated multiple geo-information technology and methods, the research would obtain valuable long-term multiple spatial and temporal scale quantity data on water and environmental concerns. Understanding of quantitative mechanism-based research methods, it is very important not only for scientific theory, but also helps to address natural and artificial groundwater recharge mechanisms, drainage analysis and a series of theoretical and practical problems for water-saving agriculture. Moreover, for evaluation of regional water resources system, it is of great practical value to develop a scientific and rational irrigation system for Guishui River in Beijing area. It is of great significance to establish a regional sustainable development pattern for balance of regional development and protection of water resources.

Study of urban heat island based on remote sensing in Beijing-capital zone

The paper focused on spatial and temporal distribution of thermal environment by Land Surface Temperature(LST) and brightness temperature retrieved from ASTER and Landsat TM/ETM in Beijing-capital zone, and analyzing scale effect of multi-resolution LST data (LST retrieved by ASTER and MODIS LST product)with the variety of landuse and NDVI. The result showed that the UHI phenomena had increasing tendency. LST waved with difference of the landuse, the highest was in bare-land, and the lowest was in water. Green island was composed mainly by forest and water, while heavy heat island and serious heat island was mainly composed by built-up and bare-land. The linear equation with a strong negative relationship between means of NDVI and means of LST( ASTER retrieval LST and MODIS LST product) associated with the five cover types has been established. Cross-validation among the LST images retrieved from ASTER and MODIS LST product are reliable. The different spatial resolution of the thermal sensors can be used in urban studies demanding different levels of details. The MODIS thermal sensor can be used for the overview of urban thermal environment. The ASTER, with its TIR 90-m resolution, can be used for more accurate monitoring thermal patterns.

Experiments of soil moisture retrieval based on Extended Kalman filter

This paper is intended to investigate the sensing of surface parameters by microwave radiometry. A Extended Kalman filter(EKF) is developed to manage the nonlinear relationship between surface parameters and radiometric signatures. Its performance of retrieving plant water content (PWC) and soil moisture content (SMC) from brightness temperatures is examined by using both predictions from model simulations and measurements from field experiments. It calculates background error covariance matrix using EKF method and is able to resolve the nonlinearity and discontinuity exist within model operator and observation operator. We optimize the observing scheme for sensing surface soil moisture (SM) from simulated brightness temperatures by the EKF. The frequencies of interest include 6.9 and 10.7 GHz of the Advanced Microwave Scanning Radiometer (AMSR), and 1.4 GHz (L-band) of the Soil Moisture and Ocean Salinity (SMOS) sensor. The Land Surface Process/Radiobrightness (LSP/R) model is used to provide time series of both SM and brightness temperatures at 6.9 and 10.7 GHz for AMSRs viewing angle of 55 degrees, and at L-band for SMOSs multiple viewing angles of 0, 10, 20, 30, 40, and 50 degrees. These multiple frequencies and viewing angles allow us to design a variety of observation modes to examine their sensitivity to SM. For example, L-band brightness temperature at any single look angle is regarded as an L-band 1D observation mode. Meanwhile, it can be combined with either the observation at other angles to become an L-band 2D mode or a multiple dimensional observation mode, or with the observation at 6.9 or 10.7 GHz to become a multiple frequency/dimensional observation mode. In this study, it is shown that the L-band 1D radiometric observation is sensitive to SM. The sensitivity can be increased by incorporating radiometric observation either from a second angle, or from multiple look angles, or from any of the two lowest AMSR channels. In addition, the advantage of an L-band 2D mode or a multiple dimensional observation mode over an L-band 1D observation mode is demonstrated. Moreover, we investigate the best observing configuration for sensing plant water content (PWC) and soil moisture content (SMC) profiles from the measured H- and V-polarized brightness temperatures at 1.4 (L-band) by the EKF. The brightness temperatures were taken by the ESTAR radiometer in SGP97 experiment. The radiometer was used to measure brightness temperatures at incident angles from −45 to 45 degrees at L-band. The SMC profiles were measured to the depths of 10 cm. The VWC was computed by Normalized Difference Vegetation Index (NDVI) values for the entire region using the TM data collected on July 2 5, 1997. The EKF was trained with observations randomly chosen from the ESTAR data of SGP97, and evaluated by the remaining data from the same set. The results indicate that the EKF can significantly improve the soil moisture estimation in the surface Iayer. And we think that the Extended Kalman filter is both practical and effective for assimilating in situ observation into land surface models.

Study of thermal environment based on remote sensing in Beijing-capital zone

The paper use the EOS-MODIS land surface temperature production (LST) to study the temporal and spatial thermal environment distribution of Bejing-capital zone, and Urban Heat island (UHI) intensity in the ten cities in the region were also studied by LST corrected by topography Characteristic. In order to find the driving factors of UHI, the relationship between urban Land cover, NDVI and LST are analyzed. The temporal analysis shows that daytime UHI demonstrates distinctive seasonal variation, while the seasonal variation of nighttime UHI is much less. The conclusion shows that the urban heat island mainly results from the difference of the surface thermal characteristics between urban and rural area, which can provide the theoretic basis for the urban-planning optimization and urban thermal environment control.