Showing papers in "International Journal of Remote Sensing in 2014"

Land-use/cover classification in a heterogeneous coastal landscape using RapidEye imagery: evaluating the performance of random forest and support vector machines classifiers

Abstract: Mapping of patterns and spatial distribution of land-use/cover (LULC) has long been based on remotely sensed data. In the recent past, efforts to improve the reliability of LULC maps have seen a proliferation of image classification techniques. Despite these efforts, derived LULC maps are still often judged to be of insufficient quality for operational applications, due to disagreement between generated maps and reference data. In this study we sought to pursue two objectives: first, to test the new-generation multispectral RapidEye imagery classification output using machine-learning random forest (RF) and support vector machines (SVM) classifiers in a heterogeneous coastal landscape; and second, to determine the importance of different RapidEye bands on classification output. Accuracy of the derived thematic maps was assessed by computing confusion matrices of the classifiers’ cover maps with respective independent validation data sets. An overall classification accuracy of 93.07% with a kappa value of ...

PROBA-V mission for global vegetation monitoring: standard products and image quality

Abstract: PROBA-V is a new global vegetation monitoring mission, to be launched in the second quarter of 2013. PROBA-V has been developed to show a consistent performance with SPOT-VEGETATION (SPOT-VGT) data, with similar spectral bands but with an improved spatial resolution of 1/3 km. The innovative mission concept has led to several key research topics related to image quality, which are discussed in this article. To support the existing VEGETATION user community, the data products for PROBA-V continue to provide daily top of canopy synthesis (S1-TOC) and 10 day synthesis products (S10-TOC). In addition, the new top of atmosphere daily synthesis (S1-TOA) products and a radiometrically/geometrically corrected (level 1C) product in raw resolution will also be provided for scientific users.

The PROBA-V mission: image processing and calibration

Abstract: With the launch of PROBA-V (Project for On-Board Autonomy – Vegetation) in 2013, the continuity and availability of global land-coverage data in four multispectral bands are ensured for the SPOT (Systeme Pour l’Observation de la Terre)-VEGETATION user community. This community has been served for already more than 14 years with high-quality 1 kilometre-resolution data. To guarantee continuation of this high quality over the full lifetime of PROBA-V, an operational processing platform and in-flight calibration algorithms have to be in place, which fully consider the specific PROBA-V platform and instrument design characteristics. Data quality has to be ensured for all available product levels, i.e. from the radiometrically corrected radiance data to the 10 day global synthesis. In this article we first focus on some specific design characteristics, which impose some challenges for data processing and calibration. Next, a technical description is given for all the processing steps such as mapping, cloud mas...

Internal solitary waves in the China seas observed using satellite remote-sensing techniques: a review and perspectives

Abstract: Internal solitary waves (ISWs) occur ubiquitously in China’s waters: the South China Sea (SCS), the East China Sea (ECS), the Yellow Sea (YS), and the Bohai Sea (BS). ISWs have long attracted much research interest because of their important role in ocean acoustics, offshore engineering, ocean mixing, primary productivity, and submarine navigation. ISWs have sea surface signatures that can be detected by satellite synthetic aperture radar (SAR) and optical sensors. Satellite remote-sensing images provide excellent two-dimensional views of the ISW field. Our understanding of ISWs in the China Seas has been greatly improved using satellite remote-sensing techniques. The primary objectives of this paper are to review the development of remote-sensing techniques in the study of ISWs and to summarize ISW characteristics in the China seas, mainly demonstrated by remote-sensing techniques. In addition, several issues with remote-sensing techniques and interesting research topics are discussed.

A phenology-based method to derive biomass production anomalies for food security monitoring in the Horn of Africa

Abstract: Monitoring vegetation conditions is a critical activity for assessing food security in the Horn of Africa. Remote sensing from space offers a unique opportunity to obtain consistent and timely information over large and often inaccessible areas where field observations are scattered, non-homogenous, or frequently unavailable. In this study we outline a method to assess objectively the performance and characteristics of seasonal vegetation development solely on the basis of time series of the fraction of absorbed photosynthetically active radiation (FAPAR) derived from Satellite Pour l’Observation de la Terre SPOT-VEGETATION (SPOT-VGT) imagery. Key phenological indicators such as the start and end of growing periods are derived from a statistical analysis of the time series to characterize the spatial and temporal evolution of successive seasons. These indicators are then utilized to compute a proxy of the seasonal gross primary production (GPP) as the cumulative FAPAR during the growing season. Vegetation...

Using earth observation-based dry season NDVI trends for assessment of changes in tree cover in the Sahel

Abstract: The co-existence of trees and grasses is a defining feature of savannah ecosystems and landscapes. During recent decades, the combined effect of climate change and increased demographic pressure has led to complex vegetation changes in these ecosystems. A number of recent Earth observation (EO)-based studies reported positive changes in biological productivity in the Sahelian region in relation to increased precipitation, triggering an increased amount of herbaceous vegetation during the rainy season. However, this ‘greening of the Sahel’ may mask changes in the tree–grass composition, with a potential reduction in tree cover having important implications for the Sahelian population. Large-scale EO-based evaluation of changes in Sahelian tree cover is assessed by analysing long-term trends in dry season minimum normalized difference vegetation index (NDVImin) derived from three different satellite sensors: Systeme Pour l’Observation de la Terre (SPOT)-VEGETATION (VGT), Terra Moderate Resolution Imaging Sp...

A global NDVI and EVI reference data set for land-surface phenology using 13 years of daily SPOT-VEGETATION observations

Abstract: Time series of vegetation indices (VIs) obtained by remote sensing are widely used to study phenology on regional and global scales. The aim of the study is to design a method and to produce a reference data set describing the seasonal and inter-annual variability of the land-surface phenology on a global scale. Specific constraints are inherent in the design of such a global reference data set: (1) the high diversity of vegetation types and the heterogeneous conditions of observation, (2) a near-daily resolution is needed to follow the rapid changes in phenology, (3) the time series used to depict the baseline vegetation cycle must be long enough to be representative of the current vegetation dynamic and encompass anomalies, and (4) a spatial resolution consistent with a land-cover-specific analysis should be privileged. This study focuses on the SPOT (Satellite Pour l'Observation de la Terre)-VEGETATION sensor and its 13-year time series of reflectance values. Five steps addressing the noise and the missing data in the reflectance time series were selected to process the daily multispectral reflectance observations. The final product provides, for every pixel, three profiles for 52 × 7-day periods: a mean, a median, and a standard deviation profile. The mean and median profiles represent the reference seasonal pattern for variation of the vegetation at a specific location whereas the standard deviation profile expresses the inter-annual variability of VIs. A quality flag at the pixel level demonstrated that the reference data set can be considered as a reliable representation of the vegetation phenology in most parts of the Earth. © 2014 Taylor & Francis.

Optical–microphysical properties of smoke haze from Siberian forest fires in summer 2012

Abstract: A comprehensive experiment on the study of dynamics of optical and microphysical characteristics of submicron aerosols in the near-ground air layer was carried out in June–August of 2012 under conditions of extremely strong smoke haze originating from vast forest fires in Siberia. Variations of the spectral angular scattering coefficients and the degree of linear polarization in the visible wavelength range are studied, as well as the mass concentrations of dry fractions of aerosol and black carbon, relative content of black carbon (BC fraction), single scattering albedo, particle size distribution function, complex refractive index of the particulate matter, and parameter of condensation activity of aerosol. Peculiarities of differences between optical and microphysical characteristics of near-ground aerosol in smoke haze and under smokeless conditions are revealed. This study is important for validation of results of remote sensing of the composition of smoke haze and background atmosphere obtained from...

Operational multi-sensor monitoring of turbidity for the entire Mekong Delta

Abstract: An operational satellite-based approach was implemented to monitor turbidity and organic absorption in the Mekong river system. Using physics-based algorithms linked together in a fully automated processing chain, more than 300 Landsat Enhanced Thematic Mapper (ETM) scenes and 1000 MODIS scenes, representing five years of data, were used to produce standardized, quantitative time series of turbidity and organic absorption across Vietnam, Thailand, Cambodia, Laos, and China. To set up this system, the specific inherent optical properties (SIOPs) of the Mekong river system were determined through three separate field campaigns, laboratory analysis, and subsequent optical closure calculations. Following this, a range of satellite data types was tested using the derived Mekong-specific inherent optical properties, including Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m data, Landsat ETM, Medium Resolution Imaging Spectrometer (MERIS), Satellite Pour l’Observation de la Terre (SPOT) 5, RapidEye, ...

Satellite-based detection of water surface variation in China’s largest freshwater lake in response to hydro-climatic drought

Abstract: Poyang Lake, the largest freshwater lake in China, is an important water resource and iconic ecosystem in a region that has been subjected to extreme drought in recent years. The lake’s inundation area is heavily influenced by basin rainfall and also by the Yangtze River’s water flows. Exploring the lake’s inundation variation in response to drought conditions is of great importance for developing effective management planning for local water resources and for mitigating future drought. Here we demonstrate how satellites can reflect the lake’s inundation changes and processes under typical hydro-climatic droughts. Using Moderate Resolution Imaging Spectroradiometer (MODIS) medium-resolution data collected between 2000 and 2011, we documented the tempo-spatial variation characteristics of water inundation areas and two typical droughts in 2006 and 2011. 2006 was a hydrologic drought year, which occurred due to an abnormal change in the Yangtze River’s water flows. A dramatic shrinkage of the inundation are...

Distribution of hotspots of chub mackerel based on remote-sensing data in coastal waters of China

Abstract: Sustainable use of fishery resources requires the effective monitoring and managing of fish stocks and fish habitats. Chub mackerel (Scomber japonicus), distributed in the East China Sea and Yellow Sea, are mainly caught by purse seine fishing fleets from China, Japan, and South Korea. This study used fishery data from Chinese large lighting–purse seine fleets and environmental data including sea surface height (SSH), sea surface temperature (SST) from remote sensing, and temperature gradient derived from SST (GSST) during 1998–2010 to develop habitat suitability index (HSI) models. The HSI models were then used to identify hotspots for chub mackerel for each month. HSI models were developed separately for each of the three distribution areas defined for chub mackerel. According to the frequency distribution of the fishing effort with respect to three environmental variables, suitability index (SI) values were calculated and SI models for each environmental variable were established. The three SI models w...

Drought impact on vegetation productivity in the Lower Mekong Basin

Abstract: The Lower Mekong Basin (LMB) has a typical monsoon climate, with high temperatures and an uneven distribution of precipitation throughout the year. This climate, combined with the geographic position of the LMB, has led to an increase in the frequency of extreme weather events over last decade. However, few previous studies have used remote-sensing data to investigate the impact of such weather events, particularly severe droughts, on biological productivity in the LMB. To address this, we assessed the impact of drought on vegetation productivity in the LMB during 2000–2011 using MOD17 products. Several drought events were identified during this period. Of these, the most severe occurred during 2005 and 2010, although the 2005 drought was both more extensive and more intense. Net primary productivity (NPP) exhibited considerable variation during 2000–2011: the droughts in 2005 and 2010 reduced NPP by 14.7% and 8.4%, respectively. The impact of drought on NPP in 2005 was much greater than that in 2010, lik...

Satellite multi-sensor mapping of suspended particulate matter in turbid estuarine and coastal ocean, China

Abstract: In this work, five ocean-colour sensors, the Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite (Terra MODIS), Moderate Resolution Imaging Spectroradiometer aboard the Aqua satellite (Aqua MODIS), Medium Range Imaging Spectrometer aboard the Environmental Satellite (Envisat MERIS), Medium Resolution Spectral Imager aboard the FY-3 satellite (FY-3 MERSI), and Geostationary Ocean Colour Imager (GOCI), were selected to examine the compatibility of an algorithm proposed for suspended particulate matter (SPM) retrieval and concordance of satellite products retrieved from different ocean-colour sensors. The results could effectively increase revisit frequency and complement a temporal gap of time series satellites that may exist between on-orbit and off-orbit. Using in situ measurements from 17 cruise campaigns between 2004 and 2012, the SPM retrieval algorithm was recalibrated so as to be universal and adapted for multi-sensor retrievals. An inter-comparison of multi-sensor-derived produc...

The PROBA-V mission: the space segment

Abstract: PROBA-V (Project for On-Board Autonomy – Vegetation) is an ESA (European Space Agency) mission developed within the framework of the Agency’s General Support Technology Programme (GSTP) devoted to the observation of the Earth’s vegetation, providing data continuity with the SPOT (Satellite pour l’Observation de la Terre) 4 and 5 VEGETATION payloads as a gap-filler to the ESA Sentinel-3 mission. The PROBA-V space segment is based on a three-axis stabilized PROBA small-satellite platform of about 140 kg equipped with a state-of-the-art compact 4-band multi-spectral imager with a large field of view. The instrument’s optomechanics is based on three very compact TMA (three mirror anastigmat) telescopes placed on an optical bench. At an altitude of 820 km, the instrument is able to provide daily coverage of the Earth in three VNIR (visible and near-infrared) bands and one SWIR (short-wave infrared) spectral band, with a spatial resolution of up to 100 m × 100 m at nadir for the VNIR. The instrument raw data wi...

Comparing global land-cover products – implications for geoscience applications: an investigation for the trans-boundary Mekong Basin

Abstract: In this article we present the results of a comparison of six globally available land-cover products for the Mekong Basin – an area that spans 795,000 km2 and comprises parts of six riparian countries: China, Myanmar, Thailand, Laos, Cambodia, and Vietnam. The basin covers most climatic zones: from high-altitude, snow-covered mountainous regions in the north, to subtropical and tropical rainforest areas and agricultural land further south. The geopolitically important region not only is home to over 72,000,000 inhabitants, but also is a centre of attention of several environmental modelling experts, trying to assess future hydrologic dynamics, climate variability, as well probable land-use developments in the area.We compare land-cover products of the University of Maryland, UMD 1992–1993, the GLC 2000 product, the GlobCover products of 2004–2006 and 2009, as well as the MODIS-derived land-cover products of 2001 and 2009. For harmonization of individual legends, the Land Cover Classification System, LCCS,...

Typhoon eye extraction with an automatic SAR image segmentation method

Abstract: Spaceborne microwave synthetic aperture radar (SAR), with its high spatial resolution (10–100 m), large area coverage, and day/night imaging capability, has been used as an important tool for typhoon monitoring. Since the microwave signal can penetrate through clouds, SAR images reveal typhoon morphology at the sea surface. Within the region of a typhoon eye, wind speed and the associated sea surface roughness are usually low. Therefore, the typhoon eye can be well distinguished as dark areas in SAR images. However, automatic typhoon eye extraction from SAR images is hampered by SAR image speckle noise and other false-alarm dark features contained in an image. In this study, we propose an image processing approach to extract typhoon eyes from SAR images. The three-step image processing includes: (1) applying an extended non-local means image denoizing algorithm to reduce image speckle noise; (2) applying a top-hat transform to denoized imagery to enhance the contrast; and (3) using a labelled watershed to...

Generation sites of internal solitary waves in the southern Taiwan Strait revealed by MODIS true-colour image observations

Abstract: Based on 12 years (2000–2011) of Moderate Resolution Imaging Spectroradiometer (MODIS) true-colour images, statistical characteristics of internal solitary waves (ISWs) in the southern Taiwan Strait were studied. Two types of ISWs with a distinct scale of wave crest length and geographic distributions were identified: Type-I waves have larger wave crest lengths and span a large area from the southern Taiwan Strait to the northern South China Sea, while Type-II waves have smaller wave crest lengths and appear only at the southeastern corner of the Taiwan Strait. Further analyses based on an empirical model of ISW propagation and on the calculations of the depth-integrated internal tide-generating body force suggested that Type-I waves mainly originate from the Luzon Strait, while Type-II waves are locally generated at the shelf break in the southeastern corner of the Taiwan Strait.

Satellite and ground-based monitoring of smoke in the atmosphere during the summer wildfires in European Russia in 2010 and Siberia in 2012

Abstract: Using Moderate Resolution Imaging Spectroradiometer (MODIS) (Aqua and Terra satellites) and in situ observations, a comparative analysis of two large-scale smoke events caused by the summer wildfires in European Russia (ER) in 2010 and Western Siberia (WS) in 2012 was carried out. In the 5-day periods of the extreme smoke pollution (5–9 August 2010 in ER and 27–31 July 2012 in WS), the number of active fires in the equal territories, confined by the coordinates 47°–65° N, 25°–55° E and 51°–70° N, 71°–104° E, was found to be 4754 for ER and 3823 for WS. With this, the regional mean aerosol optical depths (AODs) were found to be (1.02 ± 0.02) and (1.00 ± 0.04), not much differing for both the events. The regional mean aerosol radiative forcing effects at the top (R1) and the bottom (R2) of the atmosphere over ER/WS according to MODIS observations were estimated to be (−61 ± 1) and (−54 ± 2) W m−2, and (−107 ± 2) and (−96 ± 3) W m−2, respectively. At the same time, the local values of AOD and the local absol...

Validation and application of MODIS-derived SST in the South China Sea

Abstract: Using a variety of in situ sea surface temperature (SST) data sets in the South China Sea, we validate the satellite-derived SST from the Moderate Resolution Imaging Spectroradiometer (MODIS). Analysis of a large number of match-up samples during 2008-2012 shows that the MODIS SSTs have biases ranging from -0.19 degrees C to -0.34 degrees C and standard deviation (STD) errors ranging from 0.58 degrees C to 0.68 degrees C. Specifically, mean biases are all negative but there are smaller cool biases in daytime than those in night-time. The monthly validation analysis shows that the biases exhibit apparent seasonal variations. The biases in daytime have relatively small magnitudes in spring and summer, while the negative biases in night-time are most apparent in summer. On the other hand, the time series of MODIS SSTs may exhibit an evident diurnal variation for some months, which roughly agrees with the in situ SST measurements. This study also highlights that the MODIS SSTs under cloud-free conditions are effective at detecting the high-frequency and small-scale oceanic features, such as the localized diurnal variation, oceanic front, and coastal upwelling.

Interannual variability of Ulva prolifera blooms in the Yellow Sea

Abstract: A massive Ulva prolifera bloom occurred in the Yellow Sea in 2008. Since then, green tide events have occurred every year and two other massive bloom events occurred in 2009 and 2013. In this article, we investigate the spatial and temporal patterns of U. prolifera green tides in the Yellow Sea during 2007–2013 using satellite images from operational MODIS instruments on board the Terra and Aqua satellites. Satellite sea surface temperature (SST) data and sea surface wind products were analysed to study their impacts on the occurrence and evolution of the floating macroalgae. Results show that the U. prolifera blooms were most likely caused by the rapid expansion of coastal Porphyra aquaculture in Jiangsu province, China. The SST was not a controlling factor influencing the size of the algal bloom or determining the blooming time. Surface wind played a significant role on the movement and distribution of the floating macroalgae, which causes an interannual variability in the spatial and temporal patterns ...

SAR-derived wind fields at the coastal region in the East/Japan Sea and relation to coastal upwelling

Abstract: The relationship between the modification of synthetic aperture radar (SAR) wind field and coastal upwelling was investigated using high-resolution wind fields from Advanced Land Observing Satellite (ALOS) Phased Array type L-band synthetic aperture radar (PALSAR) imagery and sea-surface temperature (SST) from National Oceanic and Atmospheric Administration/Advanced Very-High-Resolution Radiometer (NOAA/AVHRR) data. The retrieved SAR wind speeds seem to agree well with in situ buoy measurements with only a relatively small error of 0.7 m s−1. The SAR wind fields retrieved from the east coast of Korea in August 2007 revealed a spatial distinction between near and offshore regions. Low wind speeds of less than 3 m s−1 were associated with cold water regions with dominant coastal upwelling. Time series of in situ measurements of both wind speed and water temperature indicated that the upwelling was induced by the wind field. The low wind field from SAR was mainly induced by changes in atmospheric stability d...

Optical closure for remote-sensing reflectance based on accurate radiative transfer approximations: the case of the Changjiang (Yangtze) River Estuary and its adjacent coastal area, China

Abstract: Optical closure exercises are pivotal for evaluating the accuracy of water quality remote-sensing techniques. The agreement between radiometrically derived and inherent optical property (IOP)-derived above-water spectral remote-sensing reflectance Rrs(λ) is necessary for resolving IOPs, the diffuse attenuation coefficient, and biogeochemical parameters from space. We combined spectral radiometric and IOP measurements to perform an optical closure exercise for two optically contrasting Chinese waters – the Changjiang (Yangtze) River Estuary and its adjacent coastal area in the East China Sea. The final aim of our investigation was to compare two derivations of Rrs(λ): Rrs(λ), derived from radiometric measurements; and Rrs(λ), derived from simultaneous IOP measurements. Five subsequent steps have been taken to achieve this goal, including (1) estimation of the Rrs(λ) from radiometric measurements; (2) scattering correction for the non-water spectral absorption coefficient apd(λ); (3) estimation of the below...

First measurements of formaldehyde integral content in the atmosphere using MAX-DOAS in the Moscow region

Abstract: We present the first observations of formaldehyde (HCHO) atmospheric column performed for Zvenigorod, Moscow region, Russia. The data were retrieved from UV spectra of the scattered solar radiation measured by the multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument developed by the Japan Agency for Marine-Earth Science and Technology. We developed an algorithm for the HCHO retrieval from these spectra. For retrieval of the HCHO differential slant column densities, we used the DOAS settings used as baseline in the Cabauw Intercomparison Campaign of Nitrogen Dioxide Measuring Instruments (CINDI). The slant column densities of HCHO were converted to vertical column densities (VCDs) using the air mass factors calculated by a radiative transfer model. The determination of HCHO in the reference spectrum used multi-axis measurements.The variability of the HCHO vertical column in 2010 is analysed. The HCHO vertical column density is larger during east wind directions than during non-east...

Preliminary validation of ocean surface vector winds estimated from China's HY-2A scatterometer

Abstract: The microwave scatterometer on the Haiyang-2A (HY-2A) satellite is designed to provide global sea surface wind field data. The accuracy of HY-2A scatterometer wind retrievals is determined through various comparisons with moored buoys and the European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis data. These comparisons were made in wide regions, including open sea and coastal areas, over a four-month period from January to March 2012 and August 2012. The retrieved wind speed results agree well with in situ observations and model data with respective biases −0.19 m s−1 and 0.01 m s−1 and root mean square error 2.02 m s−1 and 1.81 m s−1. However, the wind direction errors are a little higher. The overall bias and root mean square deviation of wind direction are −2.24°, 1.74°, and 40.28°, 38.56°, respectively. The wind speed and direction residuals are higher in low- and high-wind speed ranges. In addition, the wind speed and direction are relatively more accurate for open sea than those in...

Shoreline movement monitoring based on SAR images in Shanghai, China

Abstract: In this article, a divide-and-combine approach and multiscale normalized cut techniques are combined to extract water–land boundaries from synthetic aperture radar (SAR) images. A validation study shows that waterline extraction from SAR using the proposed algorithm is consistent with that derived from Landsat optical remote-sensing imagery. Analysis of six European Remote Sensing-1/2 (ERS-1/2) satellite and Envisat SAR images acquired at spring tides in Lingang New City, a new land-reclamation city in the suburb of Shanghai, China, between 1993 and 2005 shows the shoreline movement of the study region. We find that the shoreline had minimum seaward movement in the region due to natural forces between 1993 and 1996. Between 1996 and 1999, the shoreline moved more in the eastern and slower in the western part due to artificial impelling siltation and deposition of silt in the Yangtze River. Later, between 1999 and 2005, the shoreline significantly changed following commencement of a tidal flat reclamation project.

Development of polarization ratio model for sea surface wind field retrieval from TerraSAR-X HH polarization data

Abstract: In this article, the polarization ratio (PR) of TerraSAR-X (TS-X) vertical–vertical (VV) and horizontal–horizontal (HH) polarization data acquired over the ocean is investigated. Similar to the PR of C-band synthetic aperture radar (SAR), the PR of X-band SAR data also shows significant dependence on incidence angle. The normalized radar cross-section (NRCS) in VV polarization data is generally larger than that in HH polarization for incidence angles above 23°. Based on the analysis, two PR models proposed for C-band SAR were retuned using TS-X dual-polarization data. A new PR model, called X-PR hereafter, is proposed as well to convert the NRCS of TS-X in HH polarization to that in VV polarization. By using the developed geophysical model functions of XMOD1 and XMOD2 and the tuned PR models, the sea surface field is retrieved from the TS-X data in HH polarization. The comparisons with in situ buoy measurements show that the combination of XMOD2 and X-PR models yields a good retrieval with a root mean squ...

The Ha Tien Plain – wetland monitoring using remote-sensing techniques

Abstract: The study investigates land-cover change in the Ha Tien Plain, once considered to be the last remaining extensive wetland area of seasonally inundated grassland in the Mekong Delta. For this purpose, two Landsat images recorded in 1991 and 2009, respectively, were classified using the C5.0 decision tree classifier. A subsequent change detection analysis revealed a significant decrease of 77% of the area classified as seasonally inundated grassland in 1991, mainly due to the conversion into agriculture, aquaculture, and forest. Since these wetlands support a high diversity of flora and a rich avifauna, there should be a focus on the protection of the last remnant patches of seasonally inundated grasslands in the Ha Tien Plain in order to preserve their biodiversity values and ecosystem functions.

East Hainan upwelling fronts detected by remote sensing and modelled in summer

Abstract: Using the Belkin and O'Reilly algorithm and high-resolution (1 km) satellite sea surface temperature (SST) and chlorophyll-a (chl-a) data from 2002 to 2011, fronts were detected off the east/northeast coast of Hainan Island, South China Sea. These fronts were mainly produced by upwelling off eastern Hainan Island, through which cold, high-salinity, high-density, and nutrient-rich bottom water was brought to the surface and subsurface and then transported to the northeast of Hainan Island by the along-shore currents. The fronts are anisotropic, with a dominant orientation SSW-NNE. A three-dimensional ocean model forced by the Quick Scatterometer (QuikSCAT) winds was employed to study the three-dimensional structure of these fronts as well as the relationship between the fronts and upwelling or summer monsoon. The results show that the front intensity (cross-frontal gradient) is strongly correlated with the along-shore local winds, and has a strong seasonal and a weak inter-annual variation with a maximum of about 0.5 degrees C km (1) at the subsurface (about 15 m) rather than the surface.

Suitability of SAR imagery for automatic flood mapping in the Lower Mekong Basin

Abstract: Flood detection and inundation mapping are amongst the most important applications for remote-sensing data. Space-borne radar systems, synthetic aperture radar (SAR) in particular, and its application for waterbody mapping have recently been subject to research in many publications. Although very good results have been achieved with such data, in some cases automatic waterbody classification based on SAR data is not feasible. Factors influencing the applicability are, e.g., local environmental conditions, roughening of water surfaces due to wind, or the satellite observation geometry. In this study, a measure for the usability of SAR imagery for flood mapping was investigated. Additionally, a method for permanent waterbody mapping was introduced. The study is based on Envisat ASAR wide swath mode (150 m spatial resolution) data of the Mekong River Basin. For the usability measure, the concept of ‘high-contrast tiles’ was established, which allows an a priori estimation of the expected accuracy of a waterb...

Ice sheet survey over Antarctica using satellite altimetry: ERS-2, Envisat, SARAL/AltiKa, the key importance of continuous observations along the same repeat orbit

Abstract: From September 2002 to October 2010, the Envisat radar altimeter surveyed Greenland and Antarctica ice sheets on a 35 day repeat orbit, providing a unique data set for ice sheet mass balance studies. Up to 85 repeat cycles are available and the whole Envisat data set may be along-track processed in order to provide height variability and trend with a good spatial resolution for the objectives of ice sheet survey.Soon, a joint Centre National d’Etudes Spatiales/Indian Space Research Organisation mission, SARAL (Satellite with Argos and AltiKa), with the AltiKa payload on board, will be launched on exactly the same orbit (less than 1 km of the nomimal orbit in the across-track direction). This will allow an extension of previous European Remote Sensing (ERS) satellite, ERS-1 and ERS-2, and Envisat missions of the European Space Agency (ESA), in particular from the point of view of ice altimetry. However, AltiKa operates in the Ka band (36.8 GHz), a higher frequency than the classical Ku band (13.6 GHz), lea...