Jean-Michel Martinez

Landuse mapping with ERS SAR interferometry

Two landuse maps and a forest map of three different areas in Europe were completed with ERS SAR interferometry. The test sites represent various geomorphological regions with different cover types. In this article, the mapping algorithms are presented, the results are summarized, and the potential and limitations of ERS SAR interferometry for landuse mapping are discussed. Overall, the results suggest that landuse classification accuracies on the order of 75% are possible with, in the best case, simultaneous forest and nonforest accuracies of around 80-85%. The presence of topography reduces the performance.

ERS INSAR data for remote sensing hilly forested areas

Abstract ERS INSAR data have proved to be of interest for forest applications. The interferometric coherence was found to be related to various land uses and forest types, while in some special cases (e.g., flat terrain) the interferometric phase has been linked to the forest height. This paper reports an investigation on the information content of the interferometric coherence over a hilly terrain supporting various land use types and large pine plantations. The approach includes the use of a Geographic Information System and multitemporal data to analyze the coherence behavior as a function of forest-type forest parameters and environmental factors such as meteorological and topographic effects. Coherence appears to be efficient to discriminate between forest types. However, topography and environmental conditions strongly affect the coherence and its estimation, pointing out the need for rejection of strong slopes areas (>15°) and the sensitivity to local meteorological/seasonal effects. Based on these observations, forest classification results are presented. Forest/nonforest discrimination is very efficient (accuracy >90%) using one-day interval acquisition. More detailed classification with discrimination between forest themes gives also good results. Then, we investigate the indirect link between coherence and forest parameters. The coherence is sensitive to the forest growth stage, making forest parameter retrieval possible using a simple straight-line model. Finally, the importance of wind upon temporal decorrelation is addressed, and a semiempirical correction is proposed.

Producing time series of river water height by means of satellite radar altimetry—a comparative study

Abstract Satellite radar altimetry is complementary to in situ limnimetric surveys as a means of estimating the water height of large rivers, lakes and flood plains. Production of water height time series by satellite radar altimetry technology requires first the selection of radar ground target locations corresponding to water body surfaces under study, i.e. the definition of “virtual limnimetric stations”. We propose to investigate qualitative and quantitative differences between three representative virtual station creation methodologies: (a) a fully manual method, (b) a semi-automatic method based on a land cover characterization that allows the water body surface under study to be located; and (c) an original fully automatic procedure that exploits a digital elevation model and an estimation of the river width. The results yielded by these three methods are comparable: maximum absolute magnitudes of water height differences being 0.46, 0.26 and 0.15 m for, respectively, 95, 90 and 80% of the water height values obtained. Moreover, more than 67% and 92% of time series jointly produced by the methods present root mean square differences lower than 20 and 50 cm, respectively. The results show that the fully automatic method developed herein provides as reliable results as the fully manual one. This opens the way to use of satellite radar altimetry for the generation of water height time series on a large scale, and considerably extends the applicability of satellite radar altimetry in hydrology. Citation Roux, E., Santos da Silva, J., Vieira Getirana, A. C., Bonnet, M.-P., Calmant, S., Martinez, J.-M. & Seyler, F. (2010) Producing time series of river water height by means of satellite radar altimetry—comparative study. Hydrol. Sci. J. 55(1), 104–120.

Measurements and modeling of vertical backscatter distribution in forest canopy

Presents the results of analysis and modeling of the airborne ranging Helsinki University of Technology Scatterometer (HUTSCAT) data obtained over an Austrian pine forest in southern France. The objective is to use high vertical resolution backscatter profiles to validate a model that is subsequently used to determine the scattering sources within a canopy and to understand the wave/tree interaction mechanisms. The backscatter coefficients derived from HUTSCAT measurements at X-band at near-normal incidence and polarizations HH, VV, and VH are analyzed. The tree crown backscatter separated from the ground backscattering shows a sensitivity of about 3 dB between 0 and 200 m/sup 3//ha. The estimation of tree height using HUTSCAT profiles gives very good results, with a mean precision of 1 m. The vertical backscatter profiles are compared with the output from the MIT/CESBIO radiative transfer (RT) model coupled with a tree growth architectural model, AMAP, which recreates tree architecture using botanical bases. An a posteriori modification to the RT model is introduced, taking into account the vertical and horizontal variability of the scattering area in order to correctly estimate the backscatter attenuation. The results show good agreement between both simulated and HUTSCAT-derived vertical backscatter distribution within the canopy. The penetration depth at near normal incidence is studied. Both simulated and experimental penetration depth are compared and appear to be of several meters, varying with the stands age.

The optical properties of river and floodplain waters in the Amazon River Basin: Implications for satellite‐based measurements of suspended particulate matter

Satellite images can now be used to assess river sediment discharge, and systematic studies over rivers and lakes are required to support such applications and document the variability of inland water optical properties at the watershed scale. The optical properties of the Amazon Basin waters were analyzed from in situ measurements of the remote sensing reflectance (Rrs) at 279 stations and downwelling diffuse attenuation coefficients (Kd) at 133 stations. Measurements of the apparent optical properties, suspended particulate matter (SPM) contents, and characteristics and colored dissolved organic matter (CDOM) absorption spectra were performed during 16 cruises along the main Amazonian Rivers draining the Andes and for some tributaries. Surface-suspended sediment granulometry and mineralogy showed a stable distribution at the catchment scale, even over large distances and between tributaries. The particle number-size distribution was best described using a segmented distribution with a slope of 2.2 for the fine range (1–15 µm), and the CDOM absorption coefficient at 440 nm varied from 1.8 to 7.9 m−1. Overall, both Rrs and Kd were strongly correlated with SPM, although strong CDOM absorption limited the use of the blue spectrum. Reflectance saturation from blue to red was observed at approximately 100 g m−3, whereas the near-infrared (NIR) wavelength enabled the monitoring of the full SPM range (5–620 g m−3). In contrast, Kd showed no saturation for SPM from green to NIR, and a linear model was calculated. The use of the reflectance ratio was investigated and shown to improve the suspended sediment concentration retrieval performance.

The significance of suspended sediment transport determination on the Amazonian hydrological scenario

Rivers play an important role in continental erosion as they are the primary agents of transferring erosion products to the ocean. Understanding rivers and their transport pathways will improve the perception of many processes of global significance, such as biogeochemical cycling of pollutants and nutrients, atmospheric CO2 drawdown, soil formation and their erosion, crust evolutionin short the interaction between the atmospheric and the lithospheric compartment of the Earth s system (Allen, 2008). This interaction is characterised by the relative proportions of mechanical degradation vs. chemical weathering, whose products are, in dissolved or solid form, transported by rivers. The sediment load of rivers is thereby controlled by catchment relief, the channel slope and its connectivity to the hill slope, but also by climatic factors such as precipitation. The latter, together with temperature, exert control over chemical weathering that is dependent on physical erosion to a degree that is yet unknown (Anderson et al., 2002; Gaillardet et al., 1999; Riebe et al., 2001). Both mechanical erosion and chemical weathering, are, however, governed by tectonic activity, which drives processes of landscape rejuvenation and preconditions the fluvial transport regime (von Blanckenburg et al., 2004). On the shorter time scale, humans may act as geomorphic agents by constructing dams and reservoirs, and changing land use by deforestation and mining (Hooke, 2000; Syvitski et al., 2005; Wilkinson and McElroy, 2007). In tropical regions around the globe, large river basins are especially concentrated, and their behaviour plays an important role in river sediment transport (Latrubesse et al., 2005). For example, the tropics represent 25% of the total continental lands and contain 57% of the

Classification of land-cover and forest types using multidate ERS tandem data acquired over hilly terrain

Repeat-pass interferometry with ERS SAR satellite appears to be very useful for land cover mapping. Using 4 ERS tandem pairs, this paper studies the results of forest mapping over hilly terrain. For a given tandem pair, it appears that coherence is far better than backscatter to discriminate forest from non-forest. Using additional pairs plus seasonal backscatter change images at appropriate seasons allows one to discriminate various classes within the forest theme with satisfactory accuracy. However, it was found that local weather effects (snow, freezing) and strong slopes degrade the classification accuracy, which should be further addressed in a global classification strategy.

Monitoring water turbidity and surface suspended sediment concentration of the Bagre Reservoir (Burkina Faso) using MODIS and field reflectance data

Abstract Monitoring turbidity and Surface Suspended Sediment Concentration (SSSC) of inland waters is essential to address several important issues: erosion, sediment transport and deposition throughout watersheds, reservoir siltation, water pollution, human health risks, etc. This is especially important in regions with limited conventional monitoring capacities such as West Africa. In this study, we explore the use of Moderate Resolution Imaging Spectroradiometer data (MODIS, MOD09Q1 and MYD09Q1 products, red (R) and near infrared (NIR) bands) to monitor turbidity and SSSC for the Bagre Reservoir in Burkina Faso. High values ​​of these parameters associated with high spatial and temporal variability potentially challenge the methodologies developed so far for less turbid waters. Field measurements (turbidity, SSSC, radiometry) are used to evaluate different radiometric indices. The NIR/R ratio is found to be the most suited to retrieve SSSC and turbidity for both in-situ spectoradiometer measurements and satellite reflectance from MODIS. The spatio temporal variability of MODIS NIR/R together with rainfall estimated by the Tropical Rainforest Measuring Mission (TRMM) and altimetry data from Jason-2 is analyzed over the Bagre Reservoir for the 2000–2015 period. It is found that rain events of the early rainy season (February-March) through mid-rainy season (August) are decisive in triggering turbidity increase. Sediment transport is observed in the reservoir from upstream to downstream between June and September. Furthermore, a significant increase of 19% in turbidity values is observed between 2000 and 2015, mainly for the July to December period. It is especially well marked for August, with the central and downstream areas showing the largest increase. The most probable hypothesis to explain this evolution is a change in land use, and particularly an increase in the amount of bare soils, which enhances particle transport by runoff.

Analysis of multitemporal MODIS and landsat 7 images acquired over amazonian floodplains lakes for suspended sediment concentrations retrieval

The objective of this paper is to analyze the spatial and temporal variabilities of the water signatures as a function of sediment concentration at the surface. Images acquired simultaneously with 3 campaigns of water measurements, conducted from high water stage to low water stages, are analyzed and discussed. The potential of ETM+ and MODIS for sediment retrieval appears clearly, especially in the red bands, for concentrations in the range of 0 to 100 mg/l, commonly encountered during most of the hydrological cycle. First retrieval attempts give RMSE errors of about 10 mg/l. We show also that phytoplancton blooms, occurring over large areas during decreasing water levels, alter especially ETM+ and should be first detected to separate them from the rest of the retrieval. These results show that Landsat and especially MODIS, because of his higher revisit frequency, are very promising for surface sediment retrieval over the large lakes of the Amazon floodplain. If accurate estimates of the Amazon mean annual liquid flows exist, intra and inter annual variations of the solid flows as well as the mechanisms driving the sediment transport from the Andes to the Atlantic are only partially characterized. Sediment transport is followed in the Amazon by a sparse network of stations, regularly collecting water samples along the river mainstreams. The case of the floodplain is of special interest, covering 300000 km² at high water, it stocks large volumes of waters, and catch temporally or definitely great amounts of sediments. The floodplain are considered as net sinks of sediments but the rates of sedimentation are not yet assessed, and thus the influence of the floodplain under the sediment transport into the Amazon mainstream remain almost unquantified. A dense network of stations measuring sediment concentrations in the floodplain would be required, but the spatial and temporal heterogeneity of the floodplain, constituted of thousands of lakes, makes it clearly unaffordable. The solution is to develop new techniques, among which earth observation satellite is very promising. Use of satellite data to interpret water color in terms of chlorophyll concentration and infer primary production is routinely used over ocean waters. Recent development aimed at develop algorithms to retrieve in turbid coastal waters both chlorophyll content and total suspended sediment (TSS) concentrations. However, very few works dealt already with the use of satellite data to monitor water quality in the Amazon basin, and these few works (1), lacked dramatically of in situ measurement to validate their conclusions. The objective of this study is to develop a robust tool to monitor TSS for the large inland freshwater systems of the Amazon floodplain. This article presents, in particular, the analysis of remote sensing data using a large dataset of water quality measurements, to assess the spatial and temporal variations of water signatures. Those data were acquired within the HYBAM program (Hydrology and Geochemistry of the Amazon basin), developed by the French Institute for the Development (IRD) for 20 years in the whole Amazon basin.

River Mixing in the Amazon as a Driver of Concentration-Discharge Relationships

Large hydrological systems aggregate compositionally different waters derived from a variety of pathways. In the case of continental-scale rivers, such aggregation occurs noticeably at confluences between tributaries. Here we explore how such aggregation can affect solute concentration-discharge (C-Q) relationships and thus obscure the message carried by these relationships in terms of weathering properties of the Critical Zone. We build up a simple model for tributary mixing to predict the behavior of C-Q relationships during aggregation. We test a set of predictions made in the context of the largest worlds river, the Amazon. In particular, we predict that the C-Q relationships of the rivers draining heterogeneous catchments should be the most “dilutional” and should display the widest hysteresis loops. To check these predictions, we compute 10 day-periodicity time series of Q and major solute (Si, Ca2+, Mg2+, K+, Na+, Cl-, SO42-) C and fluxes (F) for 13 gauging stations located throughout the Amazon basin. In agreement with the model predictions, throughout the Amazon Basin C-Q relationships of most solutes shift from fairly a “chemostatic” behavior (nearly constant C) at the Andean mountain front and in pure lowland areas, to more “dilutional” patterns (negative C-Q relationship) towards the system mouth. More prominent C-Q hysteresis loops are also observed at the most downstream stations. Altogether, this study suggests that mixing of water and solutes between different flowpaths exerts a strong control on C-Q relationships of large-scale hydrological systems.