We present data collected as part of ValHyBio- VALidation HYperspectral of a BIOgeochemical model in
the South Western Tropical Lagoon of New Caledonia, a PNTS-sponsored program dedicated to chlorophyll satellite
imaging and validation as affected by bathymetry. The specific goals of ValHyBio are to: - examine time-dependent
oceanic reflectance in relation to dynamic surface processes, - construct field/satellite reflectance-based chlorophyll
models, - investigate the feasibility of inverting the model to yield surface chlorophyll and turbidity, - validate the
biogeochemical model with field/satellite observations. In situ bio-optical parameters include absorption coefficients
by CDOM and particles, Secchi disk depth, backscattering coefficient, pigment concentration, suspended matter
concentration, and K_dPAR. They are measured every month at 5 stations, of contrasted bathymetry and bottom
reflectance, as well as at a reference station situated 4 miles offshore, and on a station over coral reefs. Remote sensing
reflectance is calculated from the absorption and backscattering coefficients and compared with satellite data.
SeaWIFS and MODIS AQUA match-ups collected over the period 1997-2010 (ValHySat-VALidation HYperspectral
SATellite database) are used. Satellite retrievals are examined as a function of bathymetry. The feasibility of a longterm
monitoring program of optical water retrieval with satellite remote sensing technique is examined in the frame of
the GOPS (South Pacific Integrated Observatory).
Tropical oligotrophic coral reef lagoons are areas of high biodiversity. Chlorophyll concentration, a proxy for
phytoplankton biomass and primary production, is useful to monitor the carbon balance in the context of the climate
change and to validate simulations by coupled biogeochemical models. Chlorophyll monitoring by Aqua/MODIS is
examined on the large tropical oligo- to mesotrophic lagoon of New Caledonia (23,900 km<sup>2</sup>). The classical OC3
algorithm developed for MODIS can only be applied in deep waters. In shallow water, when the water is clear with a
weak attenuation, the bottom reflectance influences the surface reflectance and then induces an error in the chlorophyll
determination. Here, a new OC3-type polynom, relating satellite reflectance ratios and chlorophyll, was determined from
bio-optical data collected during a cruise (Valhybio) on the R/V Alis in the frame of the Programme National de
Télédétection Spatiale. From the 22th of March to the 9th of April, data were collected during two surveys of the same
network. A total of 170 in situ bio-optical measurements in the South Western and South lagoons of New Caledonia
were obtained, within a 2 weeks interval (70 non-cloudy match-ups). Four Modis images were acquired during this
cruise with moderate to good atmospheric conditions. The new polynom gives a RMS of 14.8% and a MNB of - 9% and
gives a better representation of the "true" water column chlorophyll concentration of the New Caledonia lagoon.
Due to the complexity of the tropical terrestrial environment present in Pacific islands and the lack of ground
data, remote sensing could offer an appropriate tool for obtaining a better understanding and knowledge of
the key parameters necessary to many environmental applications. Moreover, recent sensors provide high
spatial resolution and good temporal periodicity which is suitable for the study of tropical environments.
The potentiality of an oriented-object technique for land-cover mapping will be illustrated in this paper.
Unlike traditional pixel-based classification, this technique is based on object-use topology and shape features
for the differentiation of target classes. It offers a complex "knowledge base" about classes which can be
directly formulated in classification rule sets.
The first step applied to images is "segmentation" which enables the improvement of classification accuracy
as compared with that achievable using only individual spectral signature pixels.
In fact, indices based on spectral, spatial and textural or structural parameters are explored in order to reduce
the confusion between classes. The results from the segmentation are then used to produce a classification of
The oriented-object classification technique is carried out on a section of Efate Island (Vanuatu republic)
using images acquired in 2007/2008 by Formosat-2 sensor. Finally, the accuracy of the oriented-object
classification is established with the help of ground control points.