Earth Observation Satellite

POLDER First Image

October 2, 1996

1. Text of the Press release

The French POLDER (POLarization and Directionality of the EarthÕs Reflectances) instrument was selected in 1989 to fly on the Japanese satellite ADEOS (Advanced Earth Observing Satellite), in response to the NASDA Announcement of Opportunity released in 1988. The POLDER on ADEOS program, jointly conducted by the French Space agency CNES and the Japanese Space Agency NASDA , is the first major cooperation between the two agencies in the field of Earth Environment Sciences. After the successful launch of ADEOS with the NASDA H-II launcher from the Tanegashima Space Center on August 17 and the subsequent satellite check-out operations, the first POLDER data have been acquired on September 16, received at the NASDA Earth Observation Center in Hatoyama (Japan), and then transferred to the POLDER Ground Segment in Toulouse. Initial processings led to the drawing up of Earth reflectances maps at various wavelengths. Such images are representative of marine parameters (Chlorophyll pigments, etc) for green and blue wavelengths (443, 490 nm) and of the land surface for red (670 nm) and infrared wavelengths (765, 865 nm). More refined POLDER products have also been generated using multidirectional and multipolarization observations of a given Earth target. Once the routine acquisition of POLDER data has begun (expected for mid November 1996), more than 20 products, characteristic of land surfaces, Oceans, Clouds, Aerosols, and the EarthÕs Radiation Budget will be systematically computed at the POLDER Production Center and distributed to the scientific community worlwide.

The French POLDER instrument was designed and developed by CNES in collaboration with national partners (French science laboratories, CEA, CNRS). POLDER is the first operational instrument that measures the polarization of light using a set of polarizers and that observes the EarthÕs surface and atmosphere from a wide range of angles. Thus, POLDER will collect original information on the EarthÕs Environment that the international scientific community will analyze in order to better understand the role of aerosols, clouds, the carbon cycle and other parameters in climate change. Results obtained with POLDER will contribute to the objectives of the World Climate Research Program (WCRP) and the International Geosphere Biosphere Program.

CEA: Commissariat a lÕEnergie Atomique
CNRS: Centre National de la Recherche Scientifique

2. Materials

Picture#1 (colored image over France)
THE FIRST POLDER IMAGE OVER FRANCE

This view is the very first image acquired by POLDER onboard ADEOS over France on September 16th 1996. It is a blue, green and red color composite of POLDER measurements at 443 nm, 670 nm and 865 nm. Marked differences appear between the clouds (in white) and different types of surfaces: vegetation in red, soil in brown and yellow, sea in dark blue. The bright spot in the Mediterranean sea, West of Sardaigne, is the sunglint pattern. More than 15000 such images are taken every day by POLDER on ADEOS providing a daily global coverage of the Earth in eight spectral channels of the visible and near infrared spectrum.

Picture#2 (pair of colored images over France)
THE FIRST POLARIZED IMAGE ACQUIRED BY POLDER OVER FRANCE

POLDER acquires images through eight spectral filters in the visible and near infrared spectrum and also through polarizers. This pair of images shows the same September 16th 1996 acquisition over France in natural light (left image) and polarized light (right image). Each image is a blue, green and red color composite of POLDER measurements at 443 nm, 670 nm and 865 nm.
On the conventional image, marked differences appear between the clouds (in white) and different types of surfaces: vegetation in red, soil in brown and yellow, sea in dark blue. The bright spot in the Mediterranean Sea, west of the island of Sardinia, is the sunglint pattern. On the polarized image the color blue prevails and the geographic contours can hardly be recognized. This is because the polarized light mainly results from scattering in the atmosphere which increases at shorter wavelengths. The clouds still appear in grey or white and the sunglint spot in the Mediterranean Sea corresponds to a strong polarized signal. The additional information provided by these original polarized measurements allows a better characterization of the atmospheric contribution to the signal measured at the top of the atmosphere, and thus an improvement in the determination of both surface and cloud parameters of interest.

Picture#3
FIRST SEQUENCE OF POLDER IMAGES OVER EUROPE AND NORTH AFRICA

This is the first sequence (top to bottom and left to right) of images taken by POLDER onboard ADEOS on September 16th. Each image is a blue, green and red color composite of POLDER measurements at 443 nm, 670 nm and 865 nm. Marked differences appear between the clouds (in white) and different types of surfaces: vegetation in red, soil in brown and yellow, sea in dark blue.

An examination of the same area followed from one image to the other shows large variations in intensity. In the Mediterranean Sea a bright spot corresponding to sunglint appears west of Corsica and moves southwards before disappearing near the African coast (images 1 to 3).
Owing to its wide field of view POLDER can take images of a single target successively from different viewing angles. This unique capacity allows the directional properties of the radiation reflected by land surfaces and clouds to be characterized and studied.