RADAR IMAGERY IN THE STUDY OF VEGETATION OF THE CENTRAL TAIGA ZONE

This study is devoted to testing the general applicability of radar imagery in vegetation analysis, and, in particular, to determining the potential of radar images obtained for different seasons. In plains areas intermediate-scale radar images are used to discriminate forests differing in age and stand productivity and to identify sectors where the tree stand has been partially destroyed. They also can be used as supplementary material in studying forest resources and in geological research in forested plains areas. Translated by Edward Torrey, Alexandria, VA 22308 from: Geografiya i prirodnyye resursy, 1989, No. 3, pp. 130–134.     

COMPARATIVE ANALYSIS OF FEATURES ON RADAR IMAGERY AND AERIAL PHOTOGRAPHS IN DESERT AND MOUNTAINOUS LANDSCAPES

The relative information yield of radar imagery and aerial photographs is compared for selected natural and cultural features (mountains, erosional depressions, low and high forest, desert plants and shrubs, reeds, and canals) in a number of desert and mountainous areas. The types of aerial photographic and radar equipment used are discussed and recommendations are made regarding when preference should be given to one or the other type of system. Translated by Edward Torrey, Alexandria, VA 22308 from: Vestnik Leningradskogo Universiteta, seriya 7 (geologiya, geografiya), 1989, No. 2, pp. 106–110.     

非球形冰晶的毫米波k-Ze关系研究

针对毫米波雷达处理数据的实际需要,应用离散偶极子近似法DDA,获得了非球形冰晶的后向散射及衰减截面并进行了参数化,并主要基于细化的冰云模型,假设冰晶粒子谱为Γ分布,通过模拟取样各1330次（代表1330种粒子分布）,分别计算得到了W波段（94 GHz）与Ka波段（35 GHz）毫米波雷达探测的冰云衰减系数k及雷达反射率因子Z_e,而且利用数值模拟的方法,建立了k-Z_e关系的具体表达式。计算表明,非球形和非瑞利散射对W波段毫米波雷达衰减的影响较大,而且在同样滴谱分布条件下,W波段毫米波雷达的衰减比Ka波段毫米波雷达的大几倍,此外细化的冰云模型对k-Z_e关系具有影响。本研究对中纬度非降水性冰云的毫米波雷达的衰减订正具有参考价值,并对中国的毫米波雷达应用具有借鉴作用。     

AERIAL PHOTOGRAPHIC STUDIES OF THE MARINE ECOLOGY OF THE WHITE SEA

Aerial photographic surveys of the White Sea have proven to be an effective means for studying the character of bottom relief and bottom sediments in shallow areas along its coast, particularly when film sensitive to visible radiation in the yellow-green range of the spectrum is used. More specifically, the article discusses methods of aerial photographic surveying, keys for the interpretation of different types of bottom sediments, methods of mapping underwater vegetation from air photos, and the potential of radar imagery for the indirect interpretation of bottom features. Sample interpretation maps from the White Sea are included. Translated by Edward Torrey, Alexandria, VA 22308 from Izvestiya Vsesoyuznogo Geograficheskogo Obshchestva, 1988, No. 4, pp. 314-321.     

Representation of Populated Places on Radar Imagery

Russian specialists in the application of radar imagery to the study of geographical problems survey its use in the study of urban settlements. More specifically, they are concerned with the types of patterns and tonal signatures (optical densities) manifest on centimeter-band radar imagery, corresponding to buildings and other structures of various heights, dimensions, and construction materials. Cities and smaller urban and rural settlements in Vitebsk Oblast of Belarus and Voronezh Oblast of Russia are compared with respect to such information derived from radar images. Translated by Edward Torrey, Alexandria, Virginia from: Geografiya i prirodnyye resursy, 2002, No. 4, pp. 138-140.     

One centimeter-level observations of diurnal ocean tides from global monthly mean time-variable gravity fields

A method of analyzing GRACE satellite-to-satellite ranging data is presented which accentuates signals from diurnal ocean tides and dampens signals from long-period non-tidal phenomena. We form a time series of differences between two independent monthly mean gravity solutions, one set computed from range-rate data along strictly ascending arcs and the other set computed from data along descending arcs. The solar and lunisolar diurnal tides having alias periods longer than a few months, such as K ₁, P ₁, and S ₁, present noticeable variations in the monthly ascending and descending ‘difference’ solutions, while the climate-related signals are largely cancelled. By computing tidal arguments evaluated along the actual GRACE orbits, we decompose and estimate residual tidal signals with respect to our adopted prior model GOT4.7. The adjustment in the tidal height is small yet significant, yielding maximum amplitudes of 4 cm mostly under the Antarctic ice shelves and ~1 cm in general at spatial scales of several hundred kilometer. Moreover, the results suggest there are possible 1-cm errors in the tide model even over oceans well-covered by decades of radar altimetry missions. Independent validation of such small adjustments covering wide areas, however, is difficult, particularly with limited point measurements such as tide gauge.     

G0分布下基于白化滤波的极化SAR图像CFAR检测

在已有的极化合成孔径雷达(PolSAR)图像恒虚警(CFAR)检测方法中,存在着高分辨下杂波模型适用性差的难题。为解决此问题,提出了一种G_0分布下虚警概率具有闭合解析表达形式的CFAR检测方法,并定义虚警损失率(CFAR Loss, C_L)参数用以量化评估CFAR检测方法的恒虚警保持效果。首先,在乘积模型框架下,引入了逆Gamma纹理变量假设,推导出了多视极化白化滤波(MPWF)检测量的概率密度函数(PDF)。然后,对MPWF检测量的概率密度函数积分得到了虚警概率关于CFAR检测阈值的解析表达式,并设计了相应的CFAR检测流程。最后,采用仿真数据和AIRSAR实测数据对已有方法和新方法进行了算法运行时间、检测量拟合性能及目标检测性能对比。实验结果表明,方法运行时间比已有方法缩短3至30倍,具有良好的实时性;日本玉野地区的AIRSAR实测数据结果表明G_0分布对高分辨不均匀海区具有良好的拟合性能,且新方法在G_0分布和非G_0分布海区均能有效检测出目标,鲁棒性较强,相比其他检测方法品质因数(FoM)平均高出15.78%;C_L分析结果表明新方法具有良好的恒虚警保持性能,同时指出杂波对数累积量散点距离G_0分布曲线越近,新方法的恒虚警保持效果越好。     

On safe ground? Analysis of European urban geohazards using satellite radar interferometry

Urban geological hazards involving ground instability can be costly, dangerous, and affect many people, yet there is little information about the extent or distribution of geohazards within Europe’s urban areas. A reason for this is the impracticality of measuring ground instability associated with the many geohazard processes that are often hidden beneath buildings and are imperceptible to conventional geological survey detection techniques. Satellite radar interferometry, or InSAR, offers a remote sensing technique to map mm-scale ground deformation over wide areas given an archive of suitable multi-temporal data. The EC FP7 Space project named PanGeo (2011–2014), used InSAR to map areas of unstable ground in 52 of Europe’s cities, representing ∼15% of the EU population. In partnership with Europe’s national geological surveys, the PanGeo project developed a standardised geohazard-mapping methodology and recorded 1286 instances of 19 types of geohazard covering 18,000 km². Presented here is an analysis of the results of the PanGeo-project output data, which provides insights into the distribution of European urban geohazards, their frequency and probability of occurrence. Merging PanGeo data with Eurostat’s GeoStat data provides a systematic estimate of population exposures. Satellite radar interferometry is shown to be as a valuable tool for the systematic detection and mapping of urban geohazard phenomena.     

Dependence of Waterline Mapping on Radar Frequency Used for SAR Images in Intertidal Areas

Waterline detection in the intertidal areas was investigated through synthetic aperture radar (SAR) images and field measurements. Two valuable facts were found in this letter: 1) A discrepancy of waterlines between L- and P-band airborne SAR images was discovered and investigated through precise global positioning system measurements and the theory of the SAR imaging mechanism. In the intertidal areas having low slopes, the Bragg waves resonant with the radar signal can reside in different depths depending on the radar frequency, with the result that the boundary between water and land can be mapped differently in the respective SAR images. 2) Intertidal areas covered with a water film present low radar backscatter in SAR images, which can cause mislocation of waterlines     

Probabilistic mapping of flood-induced backscatter changes in SAR time series

The information content of flood extent maps can be increased considerably by including information on the uncertainty of the flood area delineation. This additional information can be of benefit in flood forecasting and monitoring. Furthermore, flood probability maps can be converted to binary maps showing flooded and non-flooded areas by applying a threshold probability value p_F = 0.5. In this study, a probabilistic change detection approach for flood mapping based on synthetic aperture radar (SAR) time series is proposed. For this purpose, conditional probability density functions (PDFs) for land and open water surfaces were estimated from ENVISAT ASAR Wide Swath (WS) time series containing >600 images using a reference mask of permanent water bodies. A pixel-wise harmonic model was used to account for seasonality in backscatter from land areas caused by soil moisture and vegetation dynamics. The approach was evaluated for a large-scale flood event along the River Severn, United Kingdom. The retrieved flood probability maps were compared to a reference flood mask derived from high-resolution aerial imagery by means of reliability diagrams. The obtained performance measures indicate both high reliability and confidence although there was a slight under-estimation of the flood extent, which may in part be attributed to topographically induced radar shadows along the edges of the floodplain. Furthermore, the results highlight the importance of local incidence angle for the separability between flooded and non-flooded areas as specular reflection properties of open water surfaces increase with a more oblique viewing geometry.     

探地雷达在城市管线测量中的应用研究

探地雷达作为一种新的城市管线探测方法,在城市测量应用中逐步得到推广,通过使用LD9000型探地雷达对天津市部分区域进行综合管线探测和分析,阐述了探地雷达在城市管线测量中的应用原理和测量过程,得出有益建议。     

卫星雷达遥感在滑坡灾害探测和监测中的应用:挑战与对策

将卫星雷达遥感应用于滑坡灾害的探测与监测,不仅可以从空间尺度上大范围捕捉到滑坡信号,而且可以从时间尺度上以较长周期追踪滑坡的运动状态。但是,卫星雷达遥感本身的局限性和滑坡所处的复杂地形环境使这一应用面临一些挑战。对卫星雷达遥感技术的4个主要挑战进行了总结与分析,同时给出了相应的解决方案:①通过提高卫星雷达影像的空间、时间分辨率,使用较长波段雷达信号或采用增强型时间序列分析技术,可降低密集植被覆盖对相干性的影响。另外,采用像素点偏移量追踪或距离向分频干涉测量方法,可克服传统干涉测量中大梯度形变引起的相位失相干。②大气延迟对卫星遥感的影响较大,尤其是地处山区的滑坡探测和监测,利用通用型卫星雷达大气改正系统可显著减弱干涉影像的大气信号并进一步简化时间序列分析,提高缓慢运动滑坡的探测和监测质量。③对于中等分辨率的雷达影像而言,利用数字高程模型可提前量化分析雷达几何畸变（如叠掩、阴影等）引发的滑坡探测监测的适用性;而对于高分辨率的雷达影像而言,利用机器学习方法无需外部高分辨率数字高程模型即可精确识别雷达影像的阴影和叠掩区并进行掩膜,从而大幅度提高数据处理效率。④针对高坡度地区残余的地形相位引起的解缠误差,可通过基线线性组合的方法予以减弱。此外,提出了一个基于多源对地观测的滑坡探测/监测系统框架,综合卫星雷达遥感与其他对地观测数据（如地基雷达、激光雷达、全球导航定位系统）,搭建了一个自动化滑坡探测与监测系统。该研究旨在阐明卫星雷达遥感的优缺点,进一步深化其在滑坡灾害监测方面的应用和推广,引出未来侧重发展方向的思考与探讨。     

Relationship of local incidence angle with satellite radar backscatter for different surface conditions

This paper examines the relationship of C-band radar backscatter from the Advanced Synthetic Aperture Radar on board the ENVISAT satellite with the local angle of incidence, whose influence on the received signal is significant, particularly in the modes of sensor operation that use the full swath of the orbit track. Linear regression is carried out for each pixel throughout a large time series of radar data over the whole of the state of Queensland, Australia, and at Great Salt Lake, Utah, USA. In the first case, the resultant coefficients are analysed for correlation against various parameters, with regolith showing the highest correlation. Class separability analysis shows the potential to use the resultant coefficients as a supplement to absolute threshold values in order to distinguish between classes of vegetation and/or geology, where cloud cover may preclude the use of optical data. It is observed that the separability between water and land is greatly higher using the slope coefficient B than using backscatter σ⁰, which may be of great benefit in the remote sensing of water where cloud cover is present (from which radar is largely independent). This is especially the case when considering the observed overlapping of backscatter values from water, with values from aeolian sand and lacustrine and alluvial sediments, rendering the use of backscatter alone problematic. In order to test the potential use of B to map water extents, the study over the Great Salt Lake compares the classification accuracy of B against that of σ⁰. It is found that the σ₀ classification misrepresents desert, salt flat and dry lake basin areas, where the B classification differentiates these regions accurately. The resultant classification achieves a kappa statistic around 0.9, which shows very high conformance. An accurate and novel method to classify water is therefore demonstrated, which awaits the launch of anticipated improved synthetic aperture radar instruments on satellite missions in the coming few years.     

Synergistic use of multi-temporal Radarsat SAR and AWiFS data for <Emphasis Type="Italic">Rabi</Emphasis> rice identification

A national level project on kharif rice identification and acreage estimation is being carried out successfully for several states in the country. A similar methodology based on the temporal profile for identification and delineation of various land cover classes has been followed for the Rabi rice acreage estimation. To define rabi rice, rabi season in India starts from November — February to March — June. Though the main growing season is predominantly winter but the uncertainty of getting cloud free data during the season has resulted in the use of microwave data. A feasibility study was taken up for early forecasting of the rabi rice area using microwave data. Hierarchical decision rule classification technique was used for the identification of the different land cover classes. Land preparation, puddling and transplantation were the reasons for the specific backscatter of rice growing areas. The increase or decrease in the SAR backscatter due to progress in the crop phenology or due to delayed sowing respectively forms the basis for identifying the rice areas. In addition the potential of optical data of a later date has been utilized in the form of various indices from bands including MIR to distinctly separate the late sown areas and also the puddled areas from other areas. This study emphasizes the synergistic use of SAR and optical data for delineating the rabi rice areas which is of immense use in giving an early forecast.     

Forest classification and impact of BIOMASS resolution on forest area and aboveground biomass estimation

The European Space Agency (ESA) is currently implementing the BIOMASS mission as 7th Earth Explorer satellite. BIOMASS will provide for the first time global forest aboveground biomass estimates based on P-band synthetic aperture radar (SAR) imagery. This paper addresses an often overlooked element of the data processing chain required to ensure reliable and accurate forest biomass estimates: accurate identification of forest areas ahead of the inversion of radar data into forest biomass estimates.The use of the P-band data from BIOMASS itself for the classification into forest and non-forest land cover types is assessed in this paper. For airborne data in tropical, hemi-boreal and boreal forests we demonstrate that classification accuracies from 90 up to 97% can be achieved using radar backscatter and phase information. However, spaceborne data will have a lower resolution and higher noise level compared to airborne data and a higher probability of mixed pixels containing multiple land cover types. Therefore, airborne data was reduced to 50 m, 100 m and 200 m resolution. The analysis revealed that about 50–60% of the area within the resolution level must be covered by forest to classify a pixel with higher probability as forest compared to non-forest. This results in forest omission and commission leading to similar forest area estimation over all resolutions. However, the forest omission resulted in a biased underestimated biomass, which was not equaled by the forest commission. The results underline the necessity of a highly accurate pre-classification of SAR data for an accurate unbiased aboveground biomass estimation.     

A GIS-Based Model to Determine Site Suitability of Emergency Evacuation Shelters

In recent years, the increase in the number of hurricanes and other costal hazards in the US pose a tremendous threat to the residents of coastal states. According to the National Hurricane Center, Florida is the most vulnerable coastal state to hurricanes. Mitigation policies have been formulated to reduce mortality and provide emergency services by evacuating people from the hazard zone. Many of these evacuees, particularly the elderly or lower income populations, rely on evacuation shelters for temporary housing. Because of the cost and limited use, evacuation shelters are almost exclusively dual use shelters where the primary purpose of the facility is for some other public function (e.g. school, hospital, etc.). In 2000, the estimated shortage of public shelter spaces in Florida was about 1.5 million. The purpose of this study was to rank the existing and candidate shelters (schools, colleges, churches and community centers) available in the state based on their site suitability. The research questions examined in this study include: (1) How many candidate shelters are located in physically suitable areas (e.g. not in a flood prone area, not near hazardous facilities, etc.)?; (2) How many existing shelters are located in physically un suitable areas, but in socially suitable areas (situated in areas with demand)?; (3) How many alternative existing and/or candidate shelters with high/very high physical suitability are located near physically un suitable existing shelters and thus, may be better choices for a shelter?; and (4) How many existing shelters located in physically un suitable areas are not near alternative existing and/or candidate shelters? A Geographic Information System‐based suitability model integrating Weighted Linear Combination (WLC) with a Pass/Fail screening technique was implemented for the 17 counties of Southern Florida. It was found that 48% of the existing shelters are located in physically unsuitable areas. Out of all the candidate shelters, 57% are located in physically unsuitable areas. For 15 of the existing shelters in unsuitable locations, no alternative candidate or existing shelter with medium to high physical suitability exists within 10 miles (16.1 km).     

基于ASAR和ETM影像的洪水淹没分析

利用了星载的雷达系统ENVISATASAR汛期数据,结合汛期前的ETM图像,得到了不同时期水体的变化范围,实现了洪水淹没范围的研究。     

Digitized global land-sea map and access software

A computer-efficient global data file, which contains digitized information that enables identification of a given latitude/longitude defined point as over land or over water, was generated from a data base which defines the world's shoreline. The method used in the generation of this land-sea boundary data map and its data structure are discussed. The data file was originally generated on a Control Data Corporation(CDC) computer, but it has been transported to other computer systems, includingIBM, DEC/VAX, UNIVAC and Cray computers. The land-sea boundary map also includes information on islands and inland lakes. The resolution of this map is 5′×5′ or an equivalent of9 km square surface blocks at the equator. The software to access this data base is structured to be easily transportable to different computers. This data base was used in the generation of the Seasat Geophysical Data Record(GDR) to identify whether a spaceborne radar altimeter measurement was over-land or over-ocean.