Valery Gond

Dr. Valery Gond

CIRAD
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Research Focus & Metrics

Academic Career Length

30Years (1997-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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29 April 2004 in Global Change Biology
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Journal Article
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HEHugh D. Eva
Hugh D. Eva
ABAlan S. Belward
Alan S. Belward
EMEvaristo E. De Miranda
Evaristo E. De Miranda
CBCarlos Marcelo Di Bella
Carlos Marcelo Di Bella
VGValery Gond
Valery Gond
SFSteffen Fritz
Steffen Fritz
A digital land cover map of South America has been produced using remotely sensed satellite data acquired between 1995 and the year 2000. The mapping scale is defined by the 1 km spatial resolution of the map grid‐cell. In order to realize the product, different sources of satellite data were used, each source providing either a particular parameter of land cover characteristic required by the legend, or mapping a particular land cover class. The map legend is designed both to fit requirements for regional climate modelling and for studies on land cover change. The legend is also compatible with a wider, global, land cover mapping exercise, which seeks to characterize the world's land surface for the year 2000. As a first step, the humid forest domain has been validated using a sample of high‐resolution satellite images. The map demonstrates both the major incursions of agriculture into the remaining forest domains and the extensive areas of agriculture, which now dominate South America's grasslands.

30 November 2016 in Remote Sensing
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Journal Article
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AVAstrid Verhegghen
Astrid Verhegghen
HEHugh Eva
Hugh Eva
GCGuido Ceccherini
Guido Ceccherini
FAFrederic Achard
Frederic Achard
VGValery Gond
Valery Gond
PCPaolo Omar Cerutti
Paolo Omar Cerutti
In this study, the recently launched Sentinel-2 (S2) optical satellite and the active radar Sentinel-1 (S1) satellite supported by active fire data from the MODIS sensor were used to detect and monitor forest fires in the Congo Basin. In the context of a very strong El Niño event, an unprecedented outbreak of fires was observed during the first months of 2016 in open forests formations in the north of the Republic of Congo. The anomalies of the recent fires and meteorological situation compared to historical data show the severity of the drought. Burnt areas mapped by the S1 SAR and S2 Multi Spectral Instrument (MSI) sensors highlight that the fires occurred mainly in Marantaceae forests, characterized by open tree canopy cover and an extensive tall herbaceous layer. The maps show that the origin of the fires correlates with accessibility to the forest, suggesting an anthropogenic origin. The combined use of the two independent and fundamentally different satellite systems of S2 and S1 captured an extent of 36,000 ha of burnt areas, with each sensor compensating for the weakness (cloud perturbations for S2, and sensitivity to ground moisture for S1) of the other.

15 July 2006 in Journal of Geophysical Research: Atmospheres
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Journal Article
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NGNadine Gobron
Nadine Gobron
BPBernard Pinty
Bernard Pinty
OAOphélie Aussedat
Ophélie Aussedat
JCJing M. Chen
Jing M. Chen
WCWarren B. Cohen
Warren B. Cohen
JWJean‐Luc Widlowski
Jean‐Luc Widlowski
This paper discusses the quality and the accuracy of the Joint Research Center (JRC) fraction of absorbed photosynthetically active radiation (FAPAR) products generated from an analysis of Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) data. The FAPAR value acts as an indicator of the presence and state of the vegetation and it can be estimated from remote sensing measurements using a physically based approach. The quality of the SeaWiFS FAPAR products assessed in this paper capitalizes on the availability of a 6‐year FAPAR time series over the full globe. This evaluation exercise is performed in two phases involving, first, an analysis of the verisimilitude of the FAPAR products under documented environmental conditions and, second, a direct comparison of the FAPAR values with ground‐based estimations where and when the latter are available. This second phase is conducted following a careful analysis of problems arising for performing such a comparison. This results in the grouping of available field information into broad categories representing different radiative transfer regimes. This strategy greatly helps the interpretation of the results since it recognizes the various levels of difficulty and sources of uncertainty associated with the radiative sampling of different types of vegetation canopies.

1 December 2013 in Remote Sensing of Environment
Verified
Journal Article
Closed access
CGClovis Grinand
Clovis Grinand
FRFety Rakotomalala
Fety Rakotomalala
VGValery Gond
Valery Gond
RVRomuald Vaudry
Romuald Vaudry
MBMartial Bernoux
Martial Bernoux
GVGhislain Vieilledent
Ghislain Vieilledent

1 November 2010 in Biological Conservation
Verified
Journal Article
Closed access
GBGaël Briant
Gaël Briant
VGValery Gond
Valery Gond
SLSusan G.W. Laurance
Susan G.W. Laurance

28 November 2013 in The Holocene
Verified
Journal Article
Closed access
JAJulie Aleman
Julie Aleman
OBOlivier Blarquez
Olivier Blarquez
IBIlham Bentaleb
Ilham Bentaleb
PBPhilippe Bonté
Philippe Bonté
BBBenoit Brossier
Benoit Brossier
CFCharly Favier
Charly Favier
Fires have played an important role in creating and maintaining savannas over the centuries and are also one of the main natural disturbances in forests. The functional role of fires in savannas and forests can be investigated through examining sedimentary charcoal in order to reconstruct long-term fire history. However, the relationship between charcoal and vegetation structure in tropical grassy ecosystems remains to be elucidated. Here, we compared recent charcoal records from lake sediments in three tropical ecosystems (forest, savanna, and forest–savanna mosaic) with land cover inferred from remote-sensing images. Charcoal width-to-length (W/L) ratio is a good proxy for changes in fuel type. At one of the lakes, a significant W/L modification from values >0.5 (mainly wood) to <0.5 (~grass) was recorded simultaneously with changes in land cover. Indeed, a significant deforestation was recorded around this lake in the remote-sensing imagery between 1984 and 1994. The results also indicate that a riparian forest around a lake could act as a physical filter for charcoal accumulation; we used the mean charcoal size as a proxy to evaluate this process. Charcoal Accumulation Rates (CHAR), a burned biomass proxy, were combined with W/L ratio and the mean charcoal size to investigate the land-use history of the landscapes surrounding the study sites. This combined approach allowed us to distinguish between episodic slash-and-burn practices in the forest and managed fields or pastures burning frequently.