Multi-temporal Aerial Photographs Research Articles

Evaluation of a gully headcut retreat model using multitemporal aerial photographs and digital elevation models

[1] A large fraction of soil erosion in temperate climate systems proceeds from gully headcut growth processes. Nevertheless, headcut retreat is not well understood. Few erosion models include gully headcut growth processes, and none of the existing headcut retreat models have been tested against long-term retreat rate estimates. In this work the headcut retreat resulting from plunge pool erosion in the Channel Hillslope Integrated Landscape Development (CHILD) model is calibrated and compared to long-term evolution measurements of six gullies at the Bardenas Reales, northeast Spain. The headcut retreat module of CHILD was calibrated by adjusting the shape factor parameter to fit the observed retreat and volumetric soil loss of one gully during a 36 year period, using reported and collected field data to parameterize the rest of the model. To test the calibrated model, estimates by CHILD were compared to observations of headcut retreat from five other neighboring gullies. The differences in volumetric soil loss rates between the simulations and observations were less than 0.05 m3 yr−1, on average, with standard deviations smaller than 0.35 m3 yr−1. These results are the first evaluation of the headcut retreat module implemented in CHILD with a field data set. These results also show the usefulness of the model as a tool for simulating long-term volumetric gully evolution due to plunge pool erosion.

항공사진을 이용한 훼손 산지 탐지 연구

사회 변화에 따라 산지이용 수요가 증가하고 다양화되면서 산림을 훼손하고, 타 용도로 활용하는 산지의 면적이 증가하고 있다. 이에 최근 훼손된 산지의 면적을 효과적으로 확인하기 위하여 두 시기의 항공사진을 활용한 훼손산지 변화탐지 기법을 연구하였다. 본 연구에서 개발한 기법은 객체기반 변화탐지 형식으로, 영상 혼합 - 객체 분할 - 객체 병합 - 노이즈 제거 - 훼손지 추출의 5가지 단계로 진행되었다. 훼손 산지에 적합한 객체생성 수준을 선정하고, 객체를 분할·병합하는 과정을 통해 객체 간의 관계와 각 객체가 지닌 분광 특성 및 정황적(Contextual) 정보를 활용하여 신규 훼손 산지를 추출하였다. 시범 영역 테스트 결과, 전체 판독범위의 12%에 해당하는 훼손 산지를 추출하였고 육안판독 훼손산지의 평균 96%를 포함함으로써, 육안판독 전·후의 보완 자료로서의 가치와 자동추출의 가능성을 확인하였다.

Denudation processes and landforms map of the Camastra River catchment (Basilicata – South Italy)

This paper performs denudation processes and landforms characterizing the Camastra River catchment (Basilicata – South Italy), on a 1:40,000 scale map. The map, which includes gravitational processes and landforms and water erosion processes and landforms, was obtained by combining field surveys with the analysis of topographic maps and of multi-temporal aerial photos, ranging from 1954 to 2010. These latter provided information on both spatial and temporal evolution of geomorphic processes. The integration and the elaboration of the data obtained in a GIS environment provided the inventory map of denudation processes and landforms. Landslides are widespread in the study area, and play an important role in the present-day landscape evolution. A total of 953 landslides were recognized, occupying a surface of 79 km2, about 22% of the whole study area. The recognized landslides were mapped on the basis of movement type, as follows: slides, flows, falls and complex landslides. With regard to water erosion processes, the most evident and spectacular landforms in the study area are represented by badlands (the so called calanchi), due to concentration of running water on steep clayey slopes, producing narrow and knife-edge ridges. Finally, sheet, rill and gully erosion are particularly active on areas devoid of vegetation cover, as well as on cultivated fields. This kind of map is an useful tool for land planning policy. Also, these types of studies are basic and complementary to applied methods for investigation and mapping of land susceptibility to denudation processes, as landslides and water erosion.

Shoreline changes interpreted from multi-temporal aerial photographs and high resolution satellite images: Wotje Atoll, Marshall Islands

Wotje Atoll is located at 9°25′N and 170°04′E within the Republic of the Marshall Islands in the central Pacific Ocean. As on other atolls, the islands perched along the rim of Wotje are low-lying and considered highly vulnerable to the impacts of climate change. A widely anticipated impact of continued sea level rise is the chronic erosion of island shorelines. Using a combination of aerial photographs and satellite imagery shoreline changes are assessed over a 67-year period characterized by rising sea level. Results indicate that between 1945 and 2010 shoreline accretion is more prevalent than erosion, with an average Net Shoreline Movement (NSM) of +1.74m, indicating accretion. Shorelines were accretionary along the lagoon, ocean and channel facing shorelines, as well as on elongate spits and small islands. A high-frequency assessment of shoreline change on a subset of islands in the east of Wotje reveals that islands were stable, with a balance between shoreline accretion and erosion. Shorelines interpreted from high resolution satellite imagery captured between 2004 and 2012 indicate that shorelines within this sample of islands are largely in an erosive state. The post-2004 shift toward erosion may be sea level rise induced, or part of an unresolved shoreline oscillation. This study demonstrates the critical need for improved shoreline change monitoring within atoll settings in order to assess sea level rise impacts along island shorelines.

多時期の空中写真から作成された数値表層モデルを用いた放牧草地における土壌侵食の地形解析

We surveyed soil erosion and slope failure in a grazed pasture in South Hokkaido using digital surface model (DSM) for geomorphic analysis, also, estimated about adaptation to a monitoring in a grazed pasture using DSM. In this study, DSMs were extracted by multi-temporal aerial photographs and digital photogrammetric technique. Digital elevation model (DEM) was extracted by contour map of paper for accuracy validation of DSM absolute accuracy. As a result of DSM accuracy evaluation on the basis of DEM, in all the ages, root mean square deviation of height direction were with satisfactory accuracy. Using extracted multi-temporal DSMs, large-scale soil erosion and slope failure were able to be performed. In addition, growths of grass were able to be grasped. However, it was difficult to extract the minute geomorphic change formed in the grazed pasture. Application of photogrammetric technique to monitoring of grazed pasture definite showed may be able to contribute to preservation of a grazed pasture, and maintenance.

多時期の空中写真から作成したＤｉｇｉｔａｌ Ｃａｎｏｐｙ Ｍｏｄｅｌによる森林キャノピーのモニタリング

Digital canopy models (DCMs) were extracted by multi-temporal aerial photographs (1964∼2004) and digital photogrammetric technique for forest canopy monitoring. In this study, ground contorol points (GCPs) were extracted by IKONOS image and digital elevation model (DEM) from LiDAR data. Bundle block adjustment with self-calibration was used for aerial triangulation, because camera callibration reports were not available. The generated DCM which was obtained in 2004 was compared with DCM from LiDAR data (obtained in 2004). Most of all pixel by aerial photographs were corresponded with DCM from LiDAR data. However, small gap areas were difficult to detect. Excluding gap areas, root mean square error of DCM from aerial photo was 3.78 meter. Using extracted multi-temporal DCMs, forest canopy changes, such as tree growth, clear-cutting and fallen damage, were figured out. Multi-temporal DCMs were found to be effective in monitoring forest canopy.

Estimating gully erosion contribution to large catchment sediment yield rate in Tanzania

The objective of this paper is to report on the issues and proposed approaches in estimating the contribution of gully erosion to sediment yield at large catchment. The case study is the upstream of Pangani River Basin (PRB) located in the North Eastern part of Tanzania. Little has been done by other researchers to study and/or extrapolate gully erosion results from plot or field scale to large catchment. In this study multi-temporal aerial photos at selected sampling sites were used to estimate gully size and morphology changes over time. The laboratory aerial photo interpretation results were groundtruthed. A data mining tool, Cubist, was used to develop predictive gully density stepwise regression models using aerial photos and environment variables. The delivery ratio was applied to estimate the sediment yield rate. The spatial variations of gully density were mapped under Arc View GIS Environment. Gully erosion sediment yield contribution was estimated as a ratio between gully erosion sediment yield and total sediment yield at the catchment outlet. The general observation is that gullies are localized features and not continuous spatially and mostly located on some mountains’ foot slopes. The estimated sediment yield rate from gullies erosion is 6800 t/year, which is about 1.6% of the long-term total catchment sediment yield rate. The result is comparable to other study findings in the same catchment. In order to improve the result larger scale aerial photos and high resolution spatial data on soil-textural class and saturated hydraulic conductivity – are recommended.

Production of vegetation spatial-structure maps by per-object analysis of juniper encroachment in multitemporal aerial photographs

The remote sensing of vegetation, which has predominantly applied methods that analyze each image pixel as independent observations, has recently seen the development of several methods that identify groups of pixels that share similar spectral or structural properties as objects. The outputs of “per-object” rather than “per-pixel” methods represent characteristics of vegetation objects, such as location, size, and volume, in a spatially explicit manner. Before decisions can be influenced by data products derived from per-object remote sensing methods, it is first necessary to adopt methodologies that can quantify the spatial and temporal trends in vegetation structure in a quantitative manner. In this study, we present one such methodological framework where (i) marked point patterns of vegetation structure are produced from two per-object methods, (ii) new spatial-structural data layers are developed via moving-window statistics applied to the point patterns, (iii) the layers are differenced to highlight spatial-structural change over a 60 year period, and (iv) the resulting difference layers are evaluated within an ecological context to describe landscape-scale changes in vegetation structure. Results show that this framework potentially provides information on the population, growth, size association (nonspatial distribution of large and small objects), and dispersion. We present an objective methodological comparison of two common per-object approaches, namely image segmentation and classification using Definiens software and two-dimensional wavelet transformations.

Monitoring deep-seated landslides by using multi-temporal aerial photographs:

Monitoring deep-seated landslides by using multi-temporal aerial photographs:

Landslide Erosion Rate in the Eastern Cordillera of Northern Bolivia

AbstractThe northeastern edge of the Bolivian Eastern Cordillera is an example of a tectonically active plateau margin where orographically enhanced precipitation facilitates very high rates of erosion. The topography of the steepest part of the margin exhibits the classic signature of high erosion rates consisting of high-relief V-shaped valleys where landsliding is the dominant process of hillslope erosion and bedrock rivers are incising into the landscape. The authors mapped landslide scars on multitemporal aerial photographs to estimate hillslope erosion rates. Field surveys of landslide scars are used to calibrate a landslide volume versus area relationship. The mapped area of landsliding, in combination with an estimate of the time for landslide scars to revegetate, leads to an erosion rate estimate. The estimated revegetation time, 10–35 yr, is based on analysis of multitemporal aerial photographs and tree rings. About 4%–6% of two watersheds in the region considered were affected by landslides over the last 10–35 yr. This result implies an erosion rate of 9 ± 5 mm yr−1 assuming that 90% of a single landslide reaches the river on average. Classified Landsat Thematic Mapper images show that landslides are occurring at approximately the same rate all across an approximately 40-km-wide swath within the high-relief zones of the cordillera.

Woody vegetation increase in Alpine areas: a proposal for a classification and validation scheme

This paper presents a change detection analysis based on a region growing segmentation approach which combines both spectral and spatial information. The test site is a French Alpine protected area, which like many other mountain areas is characterised by a general increase of forest and woody vegetation due to the abandonment of traditional land use practices. Two Landsat images of the years 1984 and 2000 were used and a classification scheme nomenclature based on four vegetation change classes, implying a gradual modification of land cover, was adopted. The accuracy of the change map was assessed both during two visits on the field and using a bi‐temporal aerial photographic coverage. A sampling scheme specifically conceived for change detection products was adopted. Error matrices and accuracy indices to assess commission and omission errors of the change maps were generated. The proposed change detection methodology circumvents limitations which are intrinsic to traditional classification procedures based only on spectral information. On the basis of the accuracy assessment, overall accuracy was 90.1% and the increase of woody vegetation turned out to be the vegetation change class better estimated, with user and producer accuracies of, respectively, 62.3% and 70%. However, confusion between the no change and the other vegetation change classes was noticed, due to standard problems encountered in change studies. Advantages and drawbacks of the use of multitemporal aerial photographs as the validation data set are also discussed.

Aerial photography and digital photogrammetry for landslide monitoring

AbstractA review is given of the techniques that are available to extract relevant information from multi-temporal aerial photographs for use in the monitoring stage of landslide assessments. It is shown that aerial photograph interpretation reveals qualitative information on surface characteristics, which is helpful in detecting landslide features and inferring the mechanisms involved. Photogrammetrically derived products can be used to quantify these processes, providing distinctive advantages. Comparison of digital elevation models (DEMs) from different times provides detailed information on changes in surface topography, whereas orthophotos can be used to measure horizontal displacements. The various factors influencing the quality of the products are also identified. Examples from a case study on the Mam Tor landslide are used to illustrate the benefits of the different approaches.

Statistical modeling of land-cover changes based on key socio-economic indicators

Landscapes are complex human–environment systems operating at spatio-temporal scales. Time is just as important as space when researching landscape changes. These changes are influenced by both environmental and socio-economic factors. However, correlations between environmental landscape attributes and land-cover patterns/changes are weakened by human activities such as intensification of agriculture eliminating the constraints of water and nutrient availability. Relations between changes in socio-economic organisation and land cover become apparent only over a longer period of time. Thus, in our study, we focused on socio-economic factors and their long-term effects on land cover. We present a method to (i) differentiate types of land-cover changes at district level, (ii) model correlations between socio-economic factors and land cover changes and (iii) identify key socio-economic indicators of land-cover changes between 1945 and 1999 in a German marginal rural landscape. We employed agricultural land-cover data gained from the interpretation of multi-temporal aerial photographs. Based on these data, we differentiated types of land-cover changes, characterising different directions of agricultural land-cover changes in the observation time period. Various socio-economic aspects were considered by introducing data representing factors of demography, employment, economy, infrastructure, agricultural structure and policy. The relations between time series of land-cover data and of socio-economic data were modeled with the help of redundancy analysis. Correlation coefficients were used to identify key socio-economic indicators of land-cover changes. The results showed that a relatively high percentage of variance in land-cover data can be explained by socio-economic factors. The types of land-cover changes can be characterised by combinations of key socio-economic indicators. The indicators can be helpful to reconstruct land-cover changes in other regions. Thus, they provide a basis for the development of sustainable land-cover management systems.

시계열 항공사진과 20세기 초 지형도를 이용한 경안천유역의 하천형태 및 하천부지 변화추세 분석

시계열 항공사진과 20세기 초 지형도를 이용한 경안천유역의 하천형태 및 하천부지 변화추세 분석

Linking socio-economic factors, environment and land cover in the German Highlands, 1945–1999

Land-cover changes are caused by human activities and natural ecological processes. Thus, our study uses an interdisciplinary approach to research land-cover changes. We present a method to (i) link socio-economic/environmental factors and land-cover changes, (ii) identify indicators of land-cover changes, and (iii) distinguish between socio-economic and environmental indicators associated with local types of overall land-cover changes. The study was conducted in the Lahn-Dill Highlands, Germany, a typical marginal rural landscape. In this region, we investigated land-cover changes occurring over the period 1945–1999. Land-cover data were derived from multi-temporal aerial photographs. Types of overall land-cover changes characterising the districts within the study area were differentiated. With the help of redundancy analysis (RDA), we analysed the relationships between land-cover changes and widely available socio-economic/environmental factors. The results reveal that both individual land-cover changes at patch level and types of overall land-cover changes characterising districts are correlated with socio-economic and environmental factors. Whereas the stable environmental factors are drivers of land-cover changes in our rural study area, socio-economic factors introduced into the analysis mostly result from land-cover changes. We identified correlative socio-economic indicators that cannot explain land-cover changes, but that in combination with the environmental factors can be used to greatly facilitate the reconstruction of past land-cover changes and thus lead to a better knowledge of land-cover history. Based on the types of overall land-cover changes, the results of the study can be adopted for the study of land-cover changes in other regions.

Analysing land-cover changes in relation to environmental variables in Hesse, Germany

Land-use and land-cover changes affect ecological landscape functions and processes. Hence, landscape ecologists have a central interest in a comprehensive understanding of such changes. Our study focuses on the relationships between environmental conditions and agricultural land-cover changes. We present a method to (i) characterise the major spatial-temporal processes of land-cover changes, (ii) identify the correlations between environmental attributes and land-cover changes and (iii) derive potential environmental drivers of land-cover changes in a German marginal rural landscape. The method was applied to study land-cover dynamics from 1945 to 1998 in the districts of Erda, Steinbrucken and Eibelshausen, situated in the marginal rural landscape of the Lahn-Dill Highlands, Germany. We employed land-cover data gained by the interpretation of multi-temporal aerial photographs. Various environmental variables were introduced into the analyses. We identified physical landscape attributes (elevation, slope, aspect, available water capacity and soil texture) and structural landscape dimensions (patch size, patch shape and distance between patch and nearest settlement). With the aid of GIS, K-means partitioning and canonical correspondence analysis, we investigated land-cover trajectory types, land-cover transitions at individual time intervals and their relationships to these environmental variables. Our results show that, between 1945 and 1998, land-cover changes correlated with the physical attributes of the underlying landscape. On the other hand, the structural landscape dimensions correlated with land cover only in periods of minor land-cover changes (1972–98). Greater diversity of physical landscape attributes is correlated with greater land-cover dynamics. Besides the important influence of socio-economic factors, land-cover changes in the study areas took place within the relatively stable physical constraints of the underlying landscape.

A spatial information technology approach for the mapping and quantification of gully erosion

In contrast to the effort during the last decades to investigate sheet (interrill) and rill soil erosion processes, relatively few studies have been focused on quantifying and/or predicting gully erosion. The extension of the use of modern spatial information technologies, such as geographical information systems (GIS), digital elevation modelling (DEM) and remote sensing, have created new possibilities for research in this field. A key issue to be addressed, as the basis for predicting the effects of global changes such as land use and climate changes, is the mapping and quantification of gully erosion rates, including rate of retreat of gully walls and rate of sediment production. This research work presents a method to compute the rate of retreat of gully walls and the associated rate of sediment production caused by gully erosion. The proposed method uses multitemporal aerial photographs and multitemporal digital elevation models, both of which have been processed using GIS techniques. The research was applied to a sample catchment of 25 km 2 located in Catalonia, Spain. Aerial photographs at scale of 1:30,000 from 1957 and orthophotos from 1993 were used to map gully erosion and determine erosion rates between 1957 and 1993. The rates of channel incision and sediment production were computed from the subtraction of multitemporal digital elevation models. The rate of gully walls retreat was 0.2 m year −1, representing a rate of 0.9‰ m 2 year −1. The maximum rate of channel incision (0.7–0.8 m year −1) occurred at the head of the gully and at meandering zones. The rate of sediment production caused by gully erosion was 1322±142 ton ha −1 year −1. In comparison with other methods to compute sediment production caused by gully erosion processes, the proposed method integrates the losses due to overland flow, mass movements and gully deepening and supposes an improvement to locate the areas within the gullies with higher erosional activity.

Assessment of the effectiveness of desertification rehabilitation measures in Yulin, north-western China using remote sensing

In China tremendous efforts have gone into the rehabilitation of desertified land for productive use such as grazing, crop cultivation and afforestation. In this study the effectiveness of these agro-ecological measures to combat desertification in Yulin, Shaanxi Province of north-western China, is evaluated from multi-temporal aerial photographs in a geographical information system (GIS). The trend of desertification between 1960 and 1987 is modelled from changes in other land covers. It is found that desertified areas have decreased by 717.91 ha during the study period as a result of rehabilitation efforts. Plantation of grass is the least effective measure for halting sand dune encroachment whereas the planting of shrubs is the most effective. The trend of desertification is most accurately modelled from the changes in grassland and farmland at an R 2 value of 0.90.

Remote sensing of savanna vegetation changes in Eastern Zambia 1972-1989

The use of the historical Landsat Multi-Spectral Scanner (MSS) archive to monitor changes in savanna vegetation between 1972 and 1989 in the South Luangwa National Park region, Eastern Zambia, was investigated. Land-cover types in the region were mapped and major changes in land cover from 1972 to 1989 were detected from MSS data. Woody canopy cover, which provides a quantitative measure of woodland structure, was estimated for woodland vegetation from MSS data using a linear relationship between woody canopy cover and red reflectance. The canopy cover changes estimated from MSS data agreed with those measured from multitemporal aerial photographs (r=0.94). Woody canopy cover changed significantly in the region from 1972 to 1989 and revealed strong spatial patterns of deforestation in Colophospermum mopane woodland on alluvial soils and vegetation regrowth of valley miombo vegetation and riverine woodland. This information on the spatial patterns of canopy cover change from 1972 to 1989 suggests certain criteria that any causative process must satisfy, and it provides a baseline for the National Park and Wildlife Services to manage the natural resources in the region. The canopy cover estimated from MSS data also provides an important input to biophysical and climatic process models for estimating the impact of vegetation structure on vegetation and climate processes.

Twenty-one years of crown area change in the Jasper Ridge Biological Preserve based on georeferenced multitemporal aerial photographs

A time series of large-scale aerial photographs of a 25 ha section of the Jasper Ridge Biological Preserve (JRBP) in California was analysed for the quantification of long-term changes in the orthogonally projected crown areas of a sample of mature canopy trees growing in closed woodland and open grassland habitats. Crown area changes were computed on the basis of pairwise image comparisons for the years 1974, 1980, 1988, 1989, 1990, 1991, 1993 and 1995. Single frame image correction methods were assessed by comparing a high-resolution physical-system based method of photogrammetric orthorectification with a low-resolution method of georeferencing that involved the use of ground control points (GCPs) for the derivation of best-fit statistical transformations. The same crown digitization procedure was used for both methods, and a statistically significant difference was not found between the high-resolution and low-resolution measured crown areas. Crown area changes were not correlated with differences in sun position at the time of aerial photo acquisition nor with differences in the off-nadir distances of each crown in the images being compared. The upper limit of digitizing error was 3.5% based on the mean coefficient of variation plus one standard deviation computed from repeat digitization measures of each crown. Crown area changes exceeding 3.5%in the pairwise image comparisons were attributed to actual crown growth or crown reduction. Expressed as a percentage of the original crown area, the mean annual rate of change for each pairwise sample period was 4.9% yr-1. In absolute terms, the mean annual rate of crown area change over the 21-year period 1974-1995 was 1.4m2 yr-1. The long-term mean annual crown growth rate of the clustered woodland trees (1.3m2yr-1) was not significantly different from the isolated grassland trees (1.5m2 yr-1). The mean annual rates of change for the periods 1974-1980, 1980-1989 and 1991-1993 were similar to the long-term average. Unusually low mean growth rates characterized the drought years of 1989-1990 and 1990-1991, while the relatively wet period of 1993-1995 exhibited the most dramatic increase in crown area at a mean rate of 3.0m2yr-1.