利用Sentinel-1A/1B雷达卫星数据监测南极接地线回退状况

南极接地线位置的准确确定对南极物质平衡计算、冰川动力学等具有重要意义。本文阐述了双差干涉测量（DDInSAR）提取接地线的基本原理,并利用欧空局Sentinel-1A/1B雷达卫星数据,基于双差干涉测量技术分别提取了东南极毛德皇后地沿岸冰架与西南极阿蒙森湾西侧Dotson冰架的接地线,将提取结果与已有接地线产品MEa-SUREs进行对比分析。结果表明,利用Sentinel-1A/1B雷达卫星数据,基于DDInSAR方法可对南极接地线进行提取及更新,并可对接地线的回退状况进行持续监测。通过监测,发现在Dotson冰架区域,接地线发生了较大的回退,1996—2018年的22年间,该区域的接地线大约回退2~5 km,其中最大回退距离达7.4 km。     

Investigation of scale dependence and geomorphic stages of evolution through hypsometric analysis: a case study of Sirsa basin,western Himalaya,India

Hypsometric analysis is an important tool to identify and justify the erosional status, erosional processes, geologic and tectonic influences, and stage of landscape development of a basin. In this study, scale dependence of hypsometric integral (Ea) and hypsometric curve parameters were derived and analysed for various order sub-basins of Sirsa river. Here, Ea of higher order sub-basins are quite scale dependent and controlled by lithology; albeit Ea of all order sub-basins is independent of tectonic uplift. Based on Ea, all fourth and fifth order sub-basins were categorised in three classes. The analysis of hypsometric curve parameters showed that sub-basins of first category (Ea < 0.35) is characterised by upward-concave curve, fluvial process dominated and early old stage landscape. Sub-basins of second category (0.35 < Ea < 0.45) reflects concave-convex curve, dominance of fluvial process and mature landscape; whereas third category sub-basins (Ea > 0.45) are diffusive process dominated and belong to late youth to early mature stage.     

IRI2016参考电离层模型在高度60～100km的精度分析

60~100 km低电离层对无线电传播、测量具有重大影响。IRI2016作为目前最新的国际参考电离层模型,研究其提供的电子密度在高度60~100 km的精度具有重要实际意义。本文以廊坊中频雷达(位于中纬度地区)提供的电子密度资料(2014—2016年)为基准,利用偏差、绝对差、相关系数、相对偏差和Lomb-Scargle周期图方法,定量分析了IRI2016模型电子密度在中纬度地区60~100 km高度范围内的精度特征。结果表明,在中纬度地区60~100 km高度范围内:①电子密度偏差、绝对差、相对偏差与季节有密切关系,在高度86~100 km,随高度增加均快速增大;相关系数同样与季节有密切关系,但随高度增加表现出增大、减小的交替变化特征;②IRI2016模型电子密度精度与太阳活动、地磁条件有关,在太阳活动低年、磁宁静条件下的电子密度精度最高;③中频雷达和IRI2016模型电子密度在82~84 km均显著(通过90%显著性检验)含有准全日潮汐波、准8 h重力波,同时IRI2016模型还显著含有准半日潮汐波,而中频雷达未显著含有准半日潮汐波;在86~92 km均显著含有准全日潮汐波、准半日潮汐波,无准8 h重力波;④中频雷达、IRI2016模型电子密度在同一高度层显著含有的波周期及功率谱存在差异,不同高度层之间显著含有的波周期及功率谱也存在差异;⑤对于高度82~92 km的中频雷达、IRI2016模型电子密度变化特征,准全日潮汐波均为主要作用,准8 h重力波在82 km为次要作用,而准半日潮汐波在86~92 km为次要作用。     

Channel pattern transformation of the Burhi‐Gandak river,Bihar, India: A study based on multidata sets

The Burhi‐Gandak river is one of the major tributaries of the Ganga River in the middle Ganga basin. The river is i known to have an oscillatory character and has changed its course in Recent times. In the present study, a variety of remote sensing data combined with surface and subsurface data have been used to delineate the fluvial palaeofeatures of this river. The palaeofeatures of the Burhi‐Gandak indicate that the river has shifted from N to S over a distance of 30 km. Further, its is observed that Burhi‐Gandak river had a larger channel width and higher discharge on earlier times and was very active. On detailed examination, a past link between the now northerly flowing Baghmati and Burhi‐Gandak rivers is detected. Based on the above features, three distinct stages of migration of the river have been identified and a summary of fluvial palaeohistory is presented.     

Estimation of Above Ground Biomass Using Texture Metrics Derived from IRS Cartosat-1 Panchromatic Data in Evergreen Forests of Western Ghats,India

Assessment of above ground forest biomass (AGB) is essential in carbon modelling studies to provide mitigation strategies as demonstrated by reducing emissions from deforestation and forest degradation. Several researchers have demonstrated the use of remote sensing data in spatial AGB estimation, in terms of spectral and radar backscatter based approaches at a landscape scale with several known limitations. However, these methods lacked the predictive ability at high biomass ranges due to saturation. The current study addresses the problem of saturation at high biomass ranges using canopy textural metric from high resolution optical data. Fourier transform based textural ordination (FOTO) technique, which involves deriving radial spectrum information via 2D fast Fourier transform and ordination through principal component analysis was used for characterizing the textural properties of forest canopies. In the current study, plot level estimated AGB from 15 (1 ha) plots was used to relate with texture derived information from very high resolution datasets (viz., IKONOS and Cartosat-1). In addition to the estimation of high biomass ranges, one of the prime objective of the current study is to understand the effects of spatial resolution on deriving textural-AGB relationship from 2.5 m IRS Cartosat data (Cartosat-A, viewing angle = ?5°) to that of IKONOS imagery with near nadir view. Further, since texture is impacted by several illumination geometry issues, the effect of viewing geometry on the relationship was evaluated using Cartosat-F (Viewing angle = 26°) imagery. The results show that the FOTO method using stereo Cartosat (A and F) images at 2.5 m resolution are able to perform well in characterizing high AGB values since the texture-biomass relationship is only subjected to 18 % relative error to that of 15 % in case of IKONOS and could aid in reduction of uncertainty in AGB estimation at a large landscape levels.     

Application of DEM,Remote Sensing and Geomorphic Studies in Identifying a Recent [or perhaps Neogene?] Upwarp in the Dibru River Basin,Assam, India

The Dibru river basin of Assam is investigated to examine the influence of active structure by applying an integrated study on geomorphology, morphotectonics, subsurface structure, Digital Elevation Model (DEM) using topographic map, IRS 1D LISS III, IRS P6 LISS III, SRTM, seismic and subsurface data. Seismic data reveals existence of an upwarp and an important fault in the basement around the central and eastern parts of the Dibru basin, respectively. The influence of these structures is well observed on all the younger formations inferring their active nature possibly till the Recent Period. Existence of fluvial anomalies, viz. annular drainage pattern, lineaments, abrupt changes in the direction of river course, beheaded stream and valley incision infer role of structural control on the fluvial features of this basin. Most commonly used indices for morphotectonic analysis, viz. basin elongation ratio (Re), transverse topographic symmetry (T), asymmetric factor (AF), valley floor width to valley height ratio (Vf) have been used to identify the evidences of active structures in the area. The values of Re indicated tectonically active, T indicated an asymmetric nature, AF indicated tilting and Vf indicated active incision in the Dibru basin. The DEM, profiles across the valley and superimposed longitudinal profiles of incised channel bed and valley shoulder of the Dibru clearly reveal valley incision by the river. Three large paleochannels located in different parts of the basin had their headwaters towards east at the common source, i.e. the Diyun river. These paleochannels had been resulted when their headwaters avulsed to create new rivers due to affect of the subsurface structures during Recent (or perhaps Neogene?) Period.     

Changing Pattern of Channel Morphology of Alaknanda River in Srinagar Valley (Garhwal Himalaya), India

The Alaknanda River is the most significant parental river of Ganga and forms an 11.5 km long and 2.5 km wide valley, locally known as the Srinagar Valley. The purpose of the present study is to highlight the recent landform changes in the Alaknanda channel course after the Kedarnath disaster, 2013. The Kedarnath flood completely changed the channel morphology of the Alaknanda river. The river changed its course at Srikot, SSB and Sriyantra Tapu with lower terraces being silted by sands at Ranihat, SSB, Bhaktiyana and Sriyantra Tapu. A new depositional terrace also formed opposite to Sriyantra Tapu. New lateral channel bars, braided channels, back swamp, rapids, pools and river souls were identified in the channel course of the river. Shifting of the channel course at Chauras still remains a serious problem for the Garhwal University Chauras Campus. About 2–5 m silt was deposited on the lower terrace at SSB, and ITI. The Srikot river bed was appended to 4.60 m. Shifting of channel course remains a serious threat to the Srinagar valley. Urbanization, sand and boulders mining, construction of dam, hydrological canal, road and settlements are the prominent example of anthropogenic activities which affect the shifting channel.     

Effects of heterogeneous land use/cover types on river channel morphology in the Solo River catchment,Eastern Uganda

In the tropics, unmonitored land use/cover types cause significant effects on the narrowing and widening of river channels which affects the integrity of water resources. River channel planform extent was characterized using Landsat images, while water and bedload samples were collected and analysed for a period of one year. The results revealed that in 1986, the channel planform covered 3.7 sq km in length than in 2013 where it increased to 4.2 sq km. Wetland (537.1mgl^?1) and bushland (186.3mgl^?1) cover types had the highest concentration of suspended sediments. Fine sand (0.25 mm), silty sand (1 mm) and silty clay (0.125 mm) bedload particle types dominated the riverbed along the channel from the sampled land use/cover types. The high concentration of sediments, bedload materials, bank instability, and streamflow were significant contributors to the narrowing and widening of the channel (p < 0.05). Agricultural land use was the major contributor of channel aggradation (0.8 m) and degradation (0.25 m) compared to tree plantations, bushlands, forest and wetland cover types.     

Use of cartographic images by expert and novice field geologists in planning fieldwork routes

Topographic maps and aerial photographs are particularly useful when geoscientists are faced with fieldwork tasks such as selecting paths for observation, establishing sampling schemes, or defining field regions. These types of images are crucial in bedrock geologic mapping, a cognitively complex field-based problem-solving task. Geologic mapping requires the geologist to correctly identify rock types and three-dimensional bedrock structures from often partial or poor-quality outcrop data while navigating through unfamiliar terrain. This paper compares the walked routes of novice to expert geologists working in the field (n = 66) with the results of a route planning and navigation survey of a similar population of geologists (n = 77). Results show clearly that those geologists with previous mapping experience make quick and decisive determinations about field areas from available imagery and maps, regardless of whether they are or not physically present in the field area. Recognition of geologic features enabled experts to form and verbalize a specific plan for travel through a landscape based on those features. Novices were less likely to develop specific travel route plans and were less likely to identify critical landscape cues from aerial photographs.     

A high-precision digital astrogeodetic traverse in an area of steep geoid gradients close to the coast of Perth,Western Australia

We present results from a new vertical deflection (VD) traverse observed in Perth, Western Australia, which is the first of its kind in the Southern Hemisphere. A digital astrogeodetic QDaedalus instrument was deployed to measure VDs with \({\sim }\)0.2\(''\) precision at 39 benchmarks with a \({{\sim }}1~\hbox {km}\) spacing. For the conversion of VDs to quasigeoid height differences, the method of astronomical–topographical levelling was applied, based on topographical information from the Shuttle Radar Topography Mission. The astronomical quasigeoid heights are in 20–30 mm (RMS) agreement with three independent gravimetric quasigeoid models, and the astrogeodetic VDs agree to 0.2–0.3\(''\) (north–south) and 0.6–0.9\(''\) (east–west) RMS. Tilt-like biases of \({\sim }1\,\,\hbox {mm}\) over \({\sim }1\,\,\hbox {km}\) are present for all quasigeoid models within \({\sim }20\,\,\hbox {km}\) of the coastline, suggesting inconsistencies in the coastal zone gravity data. The VD campaign in Perth was designed as a low-cost effort, possibly allowing replication in other Southern Hemisphere countries (e.g., Asia, Africa, South America and Antarctica), where VD data are particularly scarce.     

Scaling Effects on MODIS Band Ratio of 645 to 859 nm Aggregated from 250 m to 1 km Resolution: A Case Study in Yellow River Estuary

In this study, a theoretical model for studying the scaling effects on the two-band ratio of red to near-infrared band (TBRRN) is suggested. The model is used to explain the relationship between scaling error and local scale error; the results revealed that a special scale scaling procedure can be divided into a series smaller scale scaling procedures, and the total scaling error is the sum of the scaling error of these series’ smaller scale scaling procedure. Consequently, under the condition that the local scale is adequately fine, the total scale error at the target scale may be estimated accurately. In order to understand the mechanisms associated with scale in practical remote sensing, TBRRN data with 250 m and 1 km resolution is estimated from MODIS data at 645 and 859 nm, retrieved on September 1, 2009, in the Yellow River estuary, China. It is found that the TBRRN estimated from the 1 km resolution MODIS data is ~2.94 % smaller than as estimated from the 250 m MODIS data. The large scaling error distributes neither in the turbid waters, nor in the low suspended sediment regions, but instead in the high-low suspended sediment concentration transitional zone, which may be attributed to the spatial variable of suspended sediment in the transitional zone. This paper also points out that, owing to the importance of total scale error in achieving NASA’s mission in oceanic remote sensing, the way in which to conveniently and precisely estimate the total scale error of remote sensing parameters may potentially be an important topic in the field of oceanic remote sensing, both in present research and in the future.     

Fluvial morphometry of supraglacial river networks on the southwest Greenland Ice Sheet

Extensive, complex supraglacial river networks form on the southwest Greenland ice sheet (GrIS) surface each melt season. These networks are the dominant pathways for surface meltwater transport on this part of the ice sheet, but their fluvial morphometry has received little study. This paper utilizes high-resolution (2 m) WorldView-1/2 images, digital elevation models, and GIS tools to present a detailed morphometric characterization (river number, river length, Strahler stream order, width, depth, bifurcation ratio, braiding index, drainage density, slope, and relief ratio) for 523 GrIS supraglacial river networks. A new algorithm is presented to determine Strahler stream order in supraglacial environments. Results show that (1) Supraglacial river networks are broadly similar to terrestrial landscapes in that they follow Horton’s laws (river number, mean river length, and slope versus stream order), widen downstream, and have comparable mean bifurcation ratios (3.7 ± 1.9) and braiding indices; (2) unlike terrestrial systems, supraglacial drainage densities (0.90–4.75 km/km²) have no correlation with elevation relief, but instead display a weakly inverse correlation with ice surface elevation; (3) both well-developed (e.g., fifth-order) and discrete (e.g., first-order) supraglacial river networks form on the ice sheet, with the latter associated with short flow distances upstream of a terminal moulin; (4) mean river flow widths increase substantially, but flow depths only modestly, with increasing stream order. Viewed collectively, the 523 supraglacial river networks studied here display fluvial morphometries both similar and dissimilar to terrestrial systems, with moulin capture an important physical process driving the latter.     

Mapping the mega paleodrainage basin using shuttle radar topography mission in Eastern Sahara and its impact on the new development projects in Southern Egypt

In the current study, the shuttle radar topography mission (SRTM) data, with ～90 m horizontal resolution, were used to delineate the paleodrainage system and their mega basin extent in the East Sahara area. One mega-drainage basin has been detected, covering an area of 256 000 km2. It is classified into two sub mega basins. The Uweinate sub mega basin, which is composed of four main tributaries, collected water from a vast catchment region and drained eastward from the north, west, and southwest, starting at highland areas. The first subwatershed basin is in the northern plateau, south of the Abu-Balas area, with a total catchment area of 25 045 km2. The second subwatershed is in the Gilf Kebir plateau and has a total catchment area of 38 257 km2. The third subwatershed drains from the Uweinate highlands and has a catchment area of 46 154 km2. The fourth subwatershed, which is known in literature as Wadi Mokhtafi in its upper reach and Wadi Arid in its lower reach, drains the northwestern highlands of Sudan and has a total catchment area of 28 653 km2. The Tushka sub mega basin includes one watershed that drains from the northeast highlands of Sudan and has a total catchment area of 63 019 km2. The Uweinate and Tushka sub mega basins are joined together to the North of the Tushka depression, which drains northward toward the Kharga depression. This study indicates that the Eastern Sahara Mega Basin is a closed hydrological system independent of the other drainage systems, such as the Nile hydrosystem and the Qena Valley system. The present research illustrates the capability of the SRTM data in mapping the paleochannel networks, as well as estimate the catchment area and direction of the water flow. Finally, the study reveals that the four areas could be potentially used for different reclamation activities due to the ground water accumulations possibilities.     

Topographical Analysis of Lonar Crater Using Cartosat-1 DEM

The Lonar crater in India provides an ample opportunity to in-depth analysis of crater morphology. This paper focuses on the topographical mapping of Lonar crater with detailed study on slope, regional analysis and its rim signature. The slope of the crater (inner wall region) reveals that the northern part is steep and southern part is gentle, while, on the outer region, the northern part is flat and the later shows abrupt variations. On regional topographical mapping (~4 crater radii) around the Lonar crater, it was observed that the terrain descends from NE to SW. An elevation difference of ~20 m was observed between the N and S part, infers that the pre-impact terrain is a descending one. The crater northern rim was elevated ~10 m to ~15 m, whereas southern rim was elevated ~50 m above the average regional surface. We found that the topographically lower southern region was abruptly changed and the rim has been uplifted to an elevation of ~604 m above the average regional elevation (~555 m). This result infers that the post-impact topography was abruptly altered along the S side. The crater rim signature extracted from highest point all along the rim shows a near flat surface on north, whereas the V-shaped protrusion shows active erosion and degradation on the west. Thus, DEM based topographic study has opened a new insight about the Lonar crater, from differential rim uplift, alteration along the rim and finally revealed that the impact crater formed on a descending terrain.     

Evaluation of digital elevation models for delineation of hydrological response units in a Himalayan watershed

This study reports results from evaluation of the quality of digital elevation model (DEM) from four sources viz. topographic map (1:50,000), Shuttle Radar Topographic Mission (SRTM) (90 m), optical stereo pair from ASTER (15 m) and CARTOSAT (2.5 m) and their use in derivation of hydrological response units (HRUs) in Sitla Rao watershed (North India). The HRUs were derived using water storage capacity and slope to produce surface runoff zones. The DEMs were evaluated on elevation accuracy and representation of morphometric features. The DEM derived from optical stereo pairs (ASTER and CARTOSAT) provided higher vertical accuracies than the SRTM and topographic map-based DEM. The SRTM with a coarse resolution of 90 m provided vertical accuracy but better morphometry compared to topographic map. The HRU maps derived from the fine resolution DEM (ASTER and CARTOSAT) were more detailed but did not provide much advantage for hydrological studies at the scale of Sitla Rao watershed (5800 ha).     

Quantifying urban land cover change between 2001 and 2006 in the Gulf of Mexico region

We estimated urbanization rates (2001–2006) in the Gulf of Mexico region using the National Land Cover Database (NLCD) 2001 and 2006 impervious surface products. An improved method was used to update the NLCD impervious surface product in 2006 and associated land cover transition between 2001 and 2006. Our estimation reveals that impervious surface increased 416 km² with a growth rate of 5.8% between 2001 and 2006. Approximately 1110.1 km² of non-urban lands were converted into urban land, resulting in a 3.2% increase in the region. Hay/pasture, woody wetland, and evergreen forest represented the three most common land cover classes that transitioned to urban. Among these land cover transitions, more than 50% of the urbanization occurred within 50 km of the coast. Our analysis shows that the close-to-coast land cover transition trend, especially within 10 km off the coast, potentially imposes substantial long-term impacts on regional landscape and ecological conditions.     

Visualizing aerial wildlife movements: Internet sources of Doppler radar for the classroom

Doppler radar imagery is a useful classroom tool for studying the movement and spatio-temporal distribution of animals. In this paper we present a basic introduction to Doppler radar and the base products used to garner biological and geographical data. We draw upon imagery depicting bat and avian movements to illustrate how radar imagery may be beneficially used in the classroom to examine habitat use and species distribution at the landscape scale. Additionally we provide references for data acquisition and real-time animated imagery available on the Internet. We hope the information and imagery provided here will help instructors enrich the classroom experience for their students, while at the same time demonstrating real-world applications for the use of radar imagery in biogeographic studies.     

Remote Sensing and GIS Approach for Delineation of Groundwater Potential and Groundwater Quality Zones of Western Doon Valley, Uttarakhand, India

Groundwater exploration in the Western Doon valley has been carried out to delineate the groundwater potential and groundwater quality zones suitable for domestic purposes based on the integrated use of Remote Sensing and Geographical Information Systems (GIS). The Western Doon Valley, occupying broad synclinal troughs in the evolving fold-thrust system of sub-Himalaya, which is filled by post-Siwalik fluvial and debris flow deposits in the late Quaternary-Holocene. The Western Doon Valley area is bounded by the Mussoorie range in the north with 1800–2800 m elevation and in the south by young topographic relief of the frontal Siwalik range with ~800 m average elevation. Groundwater quality of Western Doon valley through pictorially representation in the GIS environment, it is inferred that calcium, magnesium, total hardness and nitrate at some locations above the desirable limit. The groundwater prospects map has been prepared by integrating the hydrogeomorphologic, land use/land cover from satellite data (IRS-ID, LISS-III data) slope, soil, drainage density, depth to water table of pre-monsoon and post-monsoon periods (unconfined aquifer), water table fluctuation, static water level (confined to semi-confined aquifers), specific capacity, discharge and drawdown maps using index overlay method in the GIS environment. The groundwater prospects are depicted in five categories Very high, high, moderate, low and very low (runoff zone) integrated with the groundwater quality zones which have been prepared from hydrochemical data. The results indicated that 16.82 % of the area is under Very high potential zone category with 16.11 % and 0.71 % of desirable and undesirable quality of groundwater and 18.65 %, 42.06 %, 6.96 % and 15.46 % classified as high, moderate, low and very low potential zones with desirable and undesirable quality of groundwater for domestic purposes. This study be useful for designing the groundwater prospects and management plan for the sustainable development of study area.     

长沙市景观破碎化时空分异特征研究

基于2000年长沙市1:10万土地利用图,利用ERDAS软件对1989年、2006年的遥感图像进行解译;在地理信息系统软件ArcGIS和景观格局分析软件Fragstats支持下,以城镇建设空间重心为中心,分别选取东西、南北景观样带(40 km×8 km)和8个不同半径的同心圆缓冲区,用斑块密度、边界密度、平均斑块分维数...     

Expansion dynamics of deciduous rubber plantations in Xishuangbanna,China during 2000–2010

Monoculture rubber plantations have been replacing tropical rain forests substantially in Southern China and Southeast Asia over the past several decades, which have affected human wellbeing and ecosystem services. However, to the best of our knowledge on the extent of rubber plantation expansion and their stand ages is limited. We tracked the spatiotemporal dynamics of deciduous rubber plantations in Xishuangbanna, the second largest natural rubber production region in China, from 2000 to 2010 using time-series data from the Phased Array type L-band Synthetic Aperture Radar (PALSAR), Landsat, and Moderate Resolution Imaging Spectroradiometer (MODIS). We found that rubber plantations have been expanding across a gradient from the low-elevation plains to the high elevation mountains. The areas of deciduous rubber plantations with stand ages ≤5, 6–10, and ≥11-year old were ~1.2 × 10⁵ ha, ~0.8 × 10⁵ ha, and ~2.9 × 10⁵ ha, respectively. Older rubber plantations were mainly located in low-elevation and species-rich regions (500–900 m) and younger rubber trees were distributed in areas of relative high-elevation with fragile ecosystems. Economic and market factors have driven the expansion of rubber plantations, which is not only a threat to biodiversity and environmental sustainability, but also a trigger for climatic disasters. This study illustrates that the integration of microwave, optical, and thermal data is an effective method for mapping deciduous rubber plantations in tropical mountainous regions and determining their stand ages. Our results demonstrate the spatiotemporal pattern of rubber expansions over the first decade of this century.