Unmanned Aerial Vehicles in Environmental Monitoring——An Efficient Way for Remote Sensing

Airborne photographs can be expediently used in environmental monitoring; e.g., in the surveillance of the state of natural reserve areas, such as wetlands; or in the measurement and mapping of pollutants, such as oil spills on a lake or sea. A new and cost-effective platform of airborne remote sensing is the UAV （unmanned aerial vehicle） or drone. In this experimental work, aerial photos were made in Bakony Mountains using three UAVs equipped with small HD （high definition） cameras; resolution： 1,280 ~ 720 pixels. Within the framework of this work, a small lake was photographed, where the beginning of eutrophication was detected. This hardly can be observed from ground, however, it is visible on the aerial photos. The airborne surveillance of areas of ragweed （Ambrosia sp.） populations was also investigated. It was found that both UAVs are feasible for these tasks, and the application of these platforms for environmental monitoring is advantageous, especially in case of natural reserve areas since those are very silent and--contrary to big aircrafts and helicopters---do not disturb the ecology even in natural reserve areas and the people living there. Moreover, those could be operated in a very flexible and economic way, and the aerial photos taken are highly informative.

Preparation of earthquake-triggered landslide inventory maps using remote sensing and GIS technologies:Principles and case studies

Inventory maps of earthquake-triggered landslides can be constructed using several methods,which are often subject to obvious differences due to lack of commonly accepted criteria or principles,To solve this problem,the author describes the principles for preparing inventory maps of earthquake-triggered landslides,focusing on varied methods and their criteria,The principles include the following key points：all landslides should be mapped as long as they can be recognized from images;both the boundary and source area position of landslides should be mapped;spatial distribution pattern of earthquake-triggered landslides should be continuous;complex landslides should be divided into distinct groups;three types of errors such as precision of the location and boundary of landslides,false positive errors,and false negative errors of earthquake-triggered landslide inventories should be controlled and reduced;and inventories of co-seismic landslides should be constructed by the visual interpretation method rather than automatic extraction of satellite images or/and aerial photographs,In addition,selection of remote sensing images and creation of landslides attribute database are also discussed in this paper,Then the author applies these principles to produce inventory maps of four events：the 12 May 2008 Wenchuan,China M_w 7.9,14 April 2010 Yushu,China M_w 6,9,12 January 2010 Haiti M_w7.0,and 2007 Aysen Fjord,Chile M_w 6.2,The results show obvious differences in comparison with previous studies by other researchers,which again attest to the necessity of establishment of unified principles for preparation of inventory maps of earthquake-triggered landslides.

Monitoring of Residual Forest Ecosystems Dynamics in the Mono Biosphere Reserve (Southeast Togo)

The forest ecosystems of the Lacs 2 commune (South-East, Togo) are undergoing severe degradation, which has not yet been documented. This study is carried out in order to assess and quantify the spatio-temporal dynamics of residual forests and to identify the determinants of deforestation in South East Togo. The methodological approach is based on the use of historical aerial photographs from 1976 and drone images from 2019 in addition to field investigations. Several spatial structure indices were also calculated in order to quantify the fragmentation of classes and of the forest landscape. The results show that the forest landscape is changing. The classes of forests, plantations and palm groves show an annual rate of decline of 7.5%, 0.8% and 9.4% respectively while the classes of savannahs, agglomerations, surface water and swamps increased by 16.4%, 0.4%, 0.7% and 0.1%. The results also reveal a high fragmentation within the forest, plantation, surface water and swamp class and moderate fragmentation for the savannah and palm trees classes. At the landscape level, the savannah class is dominant by more than 70%, thus making the landscape little diversified from an ecological point of view. The main driver of deforestation in the study area remains shifting slash-and-burn agriculture. It is accentuated by the establishment of perennial oil palm crops, which has influenced the annual deforestation rate by 0.72%.

Detection of Retention Trees on Clearcuts,a 50-Year Perspective

Changes in clearcut management over time were evaluated using aerial photographs taken between 1960 and 2010. Temporal changes were analysed in two different climatic zones in Sweden: a typical boreal forest zone (the coast of V&#228sterbotten County), and the hemi-boreal zone of southern Sweden (represented by Kronoberg County). The study covers the periods before and after the paradigm shift in Swedish forestry caused by the equalization of the production and nature conservation objectives specified in the first paragraph of the Swedish Forestry Act. Photographs were processed to determine clearcut size and shape and to register solitary retention trees and groups of retention trees. Small but significant changes in clearcut size were detected over time. The number of retention trees increased over time, a result that was also found in other studies using different methodologies. The results demonstrate that measurable structural changes have occurred in Swedish forests over the 25 years since the paradigm shift. Results from this study also show that digital detection of green tree retention could be a future complement to field inventory and monitoring.

Investigation of Shoreline and Topographic Change on the West Side of the Imagire-Guchi Inlet, Japan

Near the Imagire-guchi inlet, which is the target area in this study, the shoreline on the west side of a jetty retreats because of a decrease in sediment supply from the east side upstream. This study attempts to analyze the shoreline and topographic changes around the inlet through analysis of GPS （global position system） measurements and digitized shoreline from aerial photographs. In addition, the DoC （depth of closure） is determined by examining datasets of cross-shore profiles and by calculations using the Hallermeier equation （1981） based on the offshore wave height and period. The results obtained by GPS indicate coastal erosion caused by waves generated by typhoons. The gradual recovery of the shoreline position after the typhoons struck was also captured by the GPS survey. However, analysis of the aerial photographs reveals that the shoreline on the west side of the jetty fluctuated widely. The cross-shore profile datasets reveal that closure depth far from the inlet was deeper than that near the inlet.

Street Mapping of Ife Metropolis, Osun State, Nigeria

The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting information in a way that everyone would understand. Several works have taken advantage of the abilities of these technologies to produce street maps using High Resolution Images. The increase in development in Ile Ife, Osun State, Nigeria, has brought about navigation challenge and associated difficulties. This work intends to produce a street map that will ease navigation within the study area and help in road network analysis, site suitability analysis etc. Aerial Photographs, captured in the year 2009 and GeoEye1 Satellite Image of 2011 were used to extract the road network of Ife Metropolis. The image was imported into ArcGIS environment, where the database was created having feature datasets such as roads and special features. To have all the elements in vector format, the image was digitized. The street names collected from the field work was inputted into the database and then subjected to cartographical processes. 512 Roads were captured within four classes of Road Network namely Express road (5), Secondary Road (25), Primary Roads (22) and Street Road (460). This field work revealed that a larger percentage of the roads were not paved, while most of the paved ones have deteriorated and the newly constructed ones were not documented. It also showed that some of the roads were not named according to the standard and some were not named at all. From this study, we recommend that the naming system should be standardized across the study area. It is also recommended that provision should be made for street map revision on a yearly basis so as to account for changes.

Changes in land use/cover mapped over 80 years in the Highlands of Northern Ethiopia

Despite many studies on land degradation in the Highlands of Northern Ethiopia, quantitative information regarding long-term changes in land use/cover(LUC) is rare. Hence, this study aims to investigate the LUC changes in the Geba catchment(5142 km2), Northern Ethiopia, over 80 years(1935–2014). Aerial photographs(APs) of the 1930 s and Google Earth(GE) images(2014) were used. The point-count technique was utilized by overlaying a grid on APs and GE images. The occurrence of cropland, forest, grassland, shrubland, bare land, built-up areas and water body was counted to compute their fractions. A multivariate adaptive regression spline was applied to identify the explanatory factors of LUC and to create fractional maps of LUC. The results indicate significant changes of most types, except for forest and cropland. In the 1930 s, shrubland(48%) was dominant, followed by cropland(39%). The fraction of cropland in 2014(42%) remained approximately the same as in the 1930 s, while shrubland significantly dropped to 37%. Forests shrank further from a meagre 6.3% in the 1930 s to 2.3% in 2014. High overall accuracies(93% and 83%) and strong Kappa coefficients(89% and 72%) for point counts and fractional maps respectively indicate the validity of the techniques used for LUC mapping.

Improving accuracy of automated 3-D building models for smart cities

Photorealistic three-dimensional(3-D)models are important tools for urban and disaster management planning because they contain useful visual and spatial information for assessing the situation and responding accordingly.Thus,it is crucial for 3-D city models to maintain a high level of accuracy in portraying 3-D geometric objects.Despite that,significant research with respect to 3-D city models has been conducted;however,it is still difficult to create accurate 3-D representations,particularly across a wide area.Thus,this research is aimed at developing an automated 3-D city modeling application that utilizes a combination of aerial photographs,terrestrial light detection and ranging,and total station techniques for particularly dense urban areas.To enable the development of an automated 3-D city model,this research developed application software programmed in C++.This application enables users to generate 3-D images of buildings.Specifically,the 3-D city models are generated using the aerial photographs.The positional accuracy of the model is highly improved by comparing building models produced using a photogrammetric plotting instrument.Once created using a combination of aerial photos and terrestrial instruments,the 3-D city model is quantitatively assessed for completeness and suitability for commercial or public use.

Using image-based modelling(SfM–MVS)to produce a 1935 ortho-mosaic of the Ethiopian highlands

Approximately 34,000 aerial photographs covering large parts of Ethiopia and dating back to 1935–1941 have been recently recovered.These allow investigating environmental dynamics for a past period that until now is only accessible from terrestrial photographs or narratives.As the archive consists of both oblique and vertical aerial photographs that cover rather small areas,methods of image-based modelling were used to orthorectify the images.In this study,9 vertical and 18 low oblique aerial photographs were processed as an ortho-mosaic,covering an area of 25 km2,west of Wukro town in northern Ethiopia.Using 15 control points(derived from Google Earth),a Root Means Square Error of 28.5 m in X 35.4 m in Y were achieved.These values can be viewed as optimal,given the relatively low resolution and poor quality of the imagery,the lack of metadata,the geometric quality of the Google Earth imagery and the recording characteristics.Land use remained largely similar since 1936,with large parts of the land being used as cropland or extensive grazing areas.Most remarkable changes are the strong expansion of the settlements as well as land management improvements.In a larger effort,ortho-mosaics covering large parts of Ethiopia in 1935–1941 will be produced.