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POLDER (POLarization and Directionality of the Earth's Reflectances) is a passive optical imaging radiometer and polarimeter instrument developed by the French space agency CNES.

Description
The device was designed to observe solar radiation reflected by Earth's atmosphere, including studies of tropospheric aerosols, sea surface reflectance, bidirectional reflectance distribution function of land surfaces, and the Earth Radiation Budget.

Specifications
POLDER has a mass of approximately 30 kg, and has a power consumption of 77 W in imaging mode (with a mean consumption of 29 W).

Imaging
POLDER utilizes a push broom scanner. The device's optical system uses a telecentric lens and a charged coupled device matrix with a resolution of 242x548 pixels. The focal length is 3.57 mm with a focal ratio of 4.6. The field of view ranges from ±43° to ±57°, depending on the tracking method.

Spectral characteristics
The device scans between 443 and 910 nm FWHM, depending on the objective of the measurement. The shorter wavelengths (443–565 nm) typically measure ocean color, whereas the longer wavelengths (670–910 nm) are used to study vegetation and water vapor content.

Data transfer
It transmits data on 465.9875 MHz at bit rate of 200 bit/s, and receives on 401.65 MHz at 400 bit/s. The data rate is 880 kbit/s at a quantization level of 12 bits.

Missions
POLDER was first launched as a passenger instrument aboard ADEOS I on 17 August 1996. The mission ended on 30 June 1997 when communication from the host satellite failed. POLDER 2 was launched in December 2002 aboard ADEOS II. The second mission ended prematurely after 10 months when the satellite's solar panel malfunctioned. A third generation instrument was launched on board the French PARASOL microsatellite. Although the satellite has been manoeuvred out of the A-Train on 2 December 2009, data is still being acquired by the satellite.