References of "International Journal of Remote Sensing"
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See detailComparison of UAS photogrammetric products for tree detection and characterization of coniferous stands
Bonnet, Stéphanie ULg; Lisein, Jonathan ULg; Lejeune, Philippe ULg

in International Journal of Remote Sensing (2017), 38(19), 5310-5337

The use of Unmanned Aerial Systems (UAS) opens a new era for remote sensing and forest management, which requires accurate and regular quantification of resources. In this study, we propose a ... [more ▼]

The use of Unmanned Aerial Systems (UAS) opens a new era for remote sensing and forest management, which requires accurate and regular quantification of resources. In this study, we propose a comprehensive workflow to detect trees and assess forest attributes in the particular context of coniferous stands in transformation from even-aged to uneven-aged stands, using UAS imagery, from data acquisition to model construction. We implement a local maxima detection to identify the tree tops, based on a fixed-radius moving window in a Canopy Height Model (CHM) and images produced from UAS surveys. To compare the contribution of different photogrammetric products, we analysed the local maxima detected from the CHM, from three image types (individual rectified and ortho-rectified images and ortho-mosaic) and from a combination of both CHM and images. The local maxima detection gave promising results, with low omission and true-positive rates of up to 89.2%. A filtering process of false positives was implemented, using a supervised classification which decreased the false positives up to 2.6%. Based on the local maxima combined with an area-based approach, we constructed models to assess top height (R2: 83%, root mean square error [RMSE]: 5.7%), number of stems (R2: 71%, RMSE: 28.3%), basal area (R2: 70%, RMSE: 16.2%), volume (R2: 69%, RMSE: 20.1%), and individual tree height (R2: 70%, RMSE: 7.2%). Despite a suboptimal data acquisition, our simple and flexible method has yielded good results and shows great potential for application. [less ▲]

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See detailImproving specific class mapping from remotely sensed data by cost-sensitive learning
Silva, Joel; Bacao, Fernando; Dieng, Ndeye Maguette ULg et al

in International Journal of Remote Sensing (2017), 38(11), 32943316

In many remote-sensing projects, one is usually interested in a small number of land-cover classes present in a study area and not in all the land-cover classes that make-up the landscape. Previous ... [more ▼]

In many remote-sensing projects, one is usually interested in a small number of land-cover classes present in a study area and not in all the land-cover classes that make-up the landscape. Previous studies in supervised classification of satellite images have tackled specific class mapping problem by isolating the classes of interest and combining all other classes into one large class, usually called others, and by developing a binary classifier to discriminate the class of interest from the others. Here, this approach is called focused approach. The strength of the focused approach is to decompose the original multi-class supervised classification problem into a binary classification problem, focusing the process on the discrimination of the class of interest. Previous studies have shown that this method is able to discriminate more accurately the classes of interest when compared with the standard multi-class supervised approach. However, it may be susceptible to data imbalance problems present in the training data set, since the classes of interest are often a small part of the training set. A result the classification may be biased towards the largest classes and, thus, be sub-optimal for the discrimination of the classes of interest. This study presents a way to minimize the effects of data imbalance problems in specific class mapping using cost-sensitive learning. In this approach errors committed in theminority class are treated as being costlier than errors committed in the majority class. Cost-sensitive approaches are typically implemented by weighting training data points accordingly to their importance to the analysis. By changing the weight of individual data points, it is possible to shift theweight from the larger classes to the smaller ones, balancing the data set. To illustrate the use of the cost-sensitive approach to map specific classes of interest, a series of experiments with weighted support vector machines classifier and Landsat Thematic Mapper data were conducted to discriminate two types of mangrove forest (high-mangrove and low-mangrove) in Saloum estuary, Senegal, a United Nations Educational, Scientific and Cultural Organisation World Heritage site. Results suggest an increase in overall classification accuracy with the use of cost-sensitive method (97.3%) over the standard multi-class (94.3%) and the focused approach (91.0%). In particular, cost-sensitive method yielded higher sensitivity and specificity values on the discrimination of the classes of interest when compared with the standard multi-class and focused approaches. [less ▲]

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See detailObservations of asymmetric turbulent stirring in inner and marginal seas using satellite imagery
Karimova, Svetlana ULg

in International Journal of Remote Sensing (2017), 38(6), 1642-1664

For the open ocean, it was already reported on the cyclonic (anticyclonic) asymmetry of appearance of eddies of a certain spatial scale. In this article, we scrutinize the ratios of mostly mesoscale ... [more ▼]

For the open ocean, it was already reported on the cyclonic (anticyclonic) asymmetry of appearance of eddies of a certain spatial scale. In this article, we scrutinize the ratios of mostly mesoscale cyclonic and anticyclonic eddies in a number of inner and marginal marine basins, namely in the Baltic, Black, North, and Western Mediterranean Seas. As research material, over 9700 eddy manifestations in the thermal infrared, visible-range, and radar satellite imagery were used. The analysis performed showed that in all the seas the typical and average values of the diameter of anticyclonic eddies were greater than those of cyclonic eddies. The main factor that defines the ratio between anticyclonic and cyclonic eddies in the basins under consideration was discovered to be the intensity of their surface currents. Thus, in the presence of a strong jet flow at the scales of about 2–4 baroclinic Rossby radii the cyclonic eddy dominance typical for smaller eddies was replaced by the anticyclonic one. If strong jet streams were missing, as that typical of the Baltic Sea, cyclonic eddies were prevailing over the entire spectrum of eddy diameters. [less ▲]

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See detailImproved statistics of submesoscale eddies in the Baltic Sea retrieved from SAR imagery
Karimova, Svetlana ULg; Gade, Martin

in International Journal of Remote Sensing (2016), 37(10), 2394-2414

In the present paper the spatio-temporal distribution of submesoscale eddies seen in Envisat Advanced Synthetic Aperture Radar (ASAR) imagery of the Baltic Sea is discussed. A total of 1250 ASAR images ... [more ▼]

In the present paper the spatio-temporal distribution of submesoscale eddies seen in Envisat Advanced Synthetic Aperture Radar (ASAR) imagery of the Baltic Sea is discussed. A total of 1250 ASAR images acquired between 2009 and 2011 form the basis of our studies and show imprints of almost 7000 submesoscale eddies. Since the visibility of vortical structures in synthetic aperture radar (SAR) imagery significantly depends on the near-surface wind speed, wind data from a numerical model of the Baltic Sea were additionally used to get improved eddy statistics. Seasonally averaged fields of near-surface wind speed, surface currents, sea surface temperature (SST), and SST gradient were also analyzed in order to reveal the role of these hydrophysical parameters in the observed spatial and temporal variation of submesoscale eddies. [less ▲]

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See detailMonitoring surface water content using visible and short-wave infrared SPOT-5 data of wheat plots in irrigated semi-arid regions
Benabdelouahab, Tarik ULg; Balaghi, Riad; Hadria, Rachid et al

in International Journal of Remote Sensing (2015), 36(15), 4018-4036

Irrigated agriculture is an important strategic sector in arid and semi-arid regions. Given the large spatial coverage of irrigated areas, operational tools based on satellite remote sensing can ... [more ▼]

Irrigated agriculture is an important strategic sector in arid and semi-arid regions. Given the large spatial coverage of irrigated areas, operational tools based on satellite remote sensing can contribute to their optimal management. The aim of this study was to evaluate the potential of two spectral indices, calculated from SPOT-5 high-resolution visible (HRV) data, to retrieve the surface water content values (from bare soil to completely covered soil) over wheat fields and detect irrigation supplies in an irrigated area. These indices are the normalized difference water index (NDWI) and the moisture stress index (MSI), covering the main growth stages of wheat. These indices were compared to corresponding in situ measurements of soil moisture and vegetation water content in 30 wheat fields in an irrigated area of Morocco, during the 2012–2013 and 2013–2014 cropping seasons. NDWI and MSI were highly correlated with in situ measurements at both the beginning of the growing season (sowing) and at full vegetation cover (grain filling). From sowing to grain filling, the best correlation (R2 = 0.86; p < 0.01) was found for the relationship between NDWI values and observed soil moisture values. These results were validated using a k-fold cross-validation methodology; they indicated that NDWI can be used to estimate and map surface water content changes at the main crop growth stages (from sowing to grain filling). NDWI is an operative index for monitoring irrigation, such as detecting irrigation supplies and mitigating wheat water stress at field and regional levels in semi-arid areas. [less ▲]

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See detailEstimating crop-specific evapotranspiration using remote-sensing imagery at various spatial resolutions for improving crop growth modelling
Sepulcre-Cantó, Guadalupe; Gellens-Meulenberghs, Françoise; Arboleda, Alirio et al

in International Journal of Remote Sensing (2013)

By governing water transfer between vegetation and atmosphere, evapotranspiration (ET) can have a strong influence on crop yields. An estimation of ET from remote sensing is proposed by the EUMETSAT ... [more ▼]

By governing water transfer between vegetation and atmosphere, evapotranspiration (ET) can have a strong influence on crop yields. An estimation of ET from remote sensing is proposed by the EUMETSAT ‘Satellite Application Facility’ (SAF) on Land Surface Analysis (LSA). This ET product is obtained operationally every 30 min using a simplified SVAT scheme that uses, as input, a combination of remotely sensed data and atmospheric model outputs. The standard operational mode uses other LSA-SAF products coming from SEVIRI imagery (the albedo, the downwelling surface shortwave flux, and the downwelling surface longwave flux), meteorological data, and the ECOCLIMAP database to identify and characterize the land cover. With the overall objective of adapting this ET product to crop growth monitoring necessities, this study focused first on improving the ET product by integrating crop-specific information from high and medium spatial resolution remote-sensing data. A Landsat (30 m)-based crop type classification is used to identify areas where the target crop, winter wheat, is located and where crop-specific Moderate Resolution Imaging Spectroradiometer (MODIS) (250 m) time series of green area index (GAI) can be extracted. The SVAT model was run for 1 year (2007) over a study area covering Belgium and part of France using this supplementary information. Results were compared to those obtained using the standard operational mode. ET results were also compared with ground truth data measured in an eddy covariance station. Furthermore, transpiration and potential transpiration maps were retrieved and compared with those produced using the Crop Growth Monitoring System (CGMS), which is run operationally by the European Commission’s Joint Research Centre to produce in-season forecast of major European crops. The potential of using ET obtained from remote sensing to improve crop growth modelling in such a framework is studied and discussed. Finally, the use of the ET product is also explored by integrating it in a simpler modelling approach based on light-use efficiency. The Carnegie–Ames–Stanford Approach (CASA) agroecosystem model was therefore applied to obtain net primary production, dry matter productivity, and crop yield using only LSA-SAF products. The values of yield were compared with those obtained using CGMS, and the dry matter productivity values with those produced at the Flemish Institute for Technological Research (VITO). Results showed the potential of using this simplified remote-sensing method for crop monitoring. [less ▲]

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See detailReconstruction of sea surface temperature by means of DINEOF: a case study during the fishing season in the Bay of Biscay
Ganzedo, Unai; Alvera Azcarate, Aïda ULg; Esnaola, Ganix et al

in International Journal of Remote Sensing (2011), 32(4), 933-950

The Spanish surface fishery operates mainly during the summer season in the waters of the Bay of Biscay. Sea surface temperature (SST) data recovered from satellite images are being used to improve the ... [more ▼]

The Spanish surface fishery operates mainly during the summer season in the waters of the Bay of Biscay. Sea surface temperature (SST) data recovered from satellite images are being used to improve the operational efficiency of fishing vessels (e.g. reduce search time and increase catch rate) and to improve the understanding of the variations in catch distribution and rate needed to properly manage fisheries. The images used for retrieval of SST often present gaps due to the existence of clouds or satellite malfunction periods. The data gaps can totally or partially affect the area of interest. Within this study, an application of a technique for the reconstruction of missing data called DINEOF (data interpolating empirical orthogonal functions) is analysed, with the aim of testing its applicability in operational SST retrieval during summer months. In this case study, the Bay of Biscay is used as the target area. Three months of SST Moderate Resolution Imaging Spectroradiometer (MODIS) images, ranging from 1 May 2006 to 31 July 2006, were used. The main objective of this work is to test the overall performance of this technique, under potential operational use for the support of the fleet during the summer fishing season. The study is designed to analyse the sensitivity of the results of this technique to several details of the methodology used in the reconstruction of SST, such as the number of empirical orthogonal functions (EOFs) retained, the handling of the seasonal cycle or the length (number of images) of the SST database used. The results are tested against independent SST data from International Comprehensive Ocean–Atmosphere Data Set (ICOADS) ship reports and standing buoys and estimations of the error of the reconstructed SST fields are given. Conclusions show that over this area three months of data are enough for efficient SST reconstruction, which yields four EOFs as the optimal number needed for this case study. An extended EOF experiment with SST and SST with a lag of one day was carried out to analyse whether the autocorrelation of the SST data allows better performance in the SST reconstruction, although theexperiment did not improve the results. The validation studies show that the reconstructed SSTs can be trusted, even when the amount of missing data is very high. The mean absolute deviation maps show that the error is greatest near to the coast and mainly in the upwelling areas close to the French and north-western Spanish coasts. [less ▲]

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See detailAnalysis of the vegetation trends using low resolution remote sensing data in Burkina Faso (1982-1999) for the monitoring of desertification
Hountondji, Yvon ULg; Sokpon, N.; Ozer, Pierre ULg

in International Journal of Remote Sensing (2006), 27(5-6), 871-884

After about two decades of dramatic rainfall deficits that started in the late 1960s, the Sahel of West Africa has experienced increasing precipitation since the early 1990s. The implementation of the ... [more ▼]

After about two decades of dramatic rainfall deficits that started in the late 1960s, the Sahel of West Africa has experienced increasing precipitation since the early 1990s. The implementation of the United Nations Convention to Combat Desertification (UNCCD) needs the identification of areas that record declining vegetation productivity over long-time periods. In this scope, we analyse the state of the vegetation productivity using long-term time series of NOAA AVHRR NDVI data and compare it to rainfall data. For this, 128 rain gauge data (RR) were compared with the integrated NDVI during the growing period (iNDVI) values in Burkina Faso from 1982 to 1999. During the analysed period, most of the studied stations in the country were stable for the iNDVI/RR (57.8%). However, 39.8% showed a weak to strong negative trend in the iNDVI/RR while only 2.4% showed a weak positive trend. These negative trends may reflect ongoing desertification processes in Burkina Faso and could be a starting point for the identification of hot-spots areas to determine where to take action to combat desertification. [less ▲]

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See detailInvestigating the relationship between ground-measured LAI and vegetation indices in an alpine meadow, north-west China.
Lu, L; Li, X; Huang, C L et al

in International Journal of Remote Sensing (2005), 26(20), 4471-4484

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