POLDER
Encyclopedia
POLDER is a passive optical imaging radiometer
and polarimeter
developed by the French space agency CNES
.
's atmosphere, including studies of tropospheric aerosols, sea surface reflectance
, bidirectional reflectance distribution function
of land surfaces, and the Earth Radiation Budget.
. The device's optical system uses a telecentric lens
and a charged coupled device matrix with a resolution of 242x548 pixel
s. The focal length
is 3.57 millimetre (0.140551181102362 in) with a focal ratio
of 4.6. The field of view
ranges from ±43° to ±57°, depending on the tracking method.
s (443–565 nm) typically measure ocean color, whereas the longer wavelengths (670–910 nm) are used to study vegetation
and water vapor
content.
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.
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.
Radiometer
A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
and polarimeter
Polarimeter
A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance....
developed by the French space agency CNES
CNES
The is the French government space agency . Established under President Charles de Gaulle in 1961, its headquarters are located in central Paris and it is under the supervision of the French Ministries of Defence and Research...
.
Description
The device was designed to observe solar radiation reflected by EarthEarth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's atmosphere, including studies of tropospheric aerosols, sea surface reflectance
Ocean color
The "color" of the ocean is determined by the interactions of incident light with substances or particles present in the water.For pure ocean water, such like the open ocean water, it appears as a very dark navy blue. The reason the ocean is blue is due to the absorption and scattering of light...
, bidirectional reflectance distribution function
Bidirectional reflectance distribution function
The bidirectional reflectance distribution function is a four-dimensional function that defines how light is reflected at an opaque surface...
of land surfaces, and the Earth Radiation Budget.
Specifications
POLDER has a mass of approximately 30 kilograms (66.1 lb), and has a power consumption of 77 W in imaging mode (with a mean consumption of 29 W).Imaging
POLDER utilizes a push broom scannerPush broom scanner
A Push broom scanner is a technology for obtaining satellite images with optical cameras. It is used for passive remote sensing from space. In a push broom sensor, a line of sensors arranged perpendicular to the flight direction of the spacecraft is used. Different areas of the surface are imaged...
. The device's optical system uses a telecentric lens
Telecentric lens
A telecentric lens is a compound lens which has its entrance or exit pupil at infinity; in the prior case, this produces an orthographic view of the subject. This means that the chief rays are parallel to the optical axis in front of or behind the system, respectively...
and a charged coupled device matrix with a resolution of 242x548 pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s. The focal length
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
is 3.57 millimetre (0.140551181102362 in) with a focal ratio
F-number
In optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...
of 4.6. The field of view
Field of view
The field of view is the extent of the observable world that is seen at any given moment....
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 wavelengthWavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s (443–565 nm) typically measure ocean color, whereas the longer wavelengths (670–910 nm) are used to study vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
and water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
content.
Data transfer
It transmits data on 465.9875 MHz at bit rateBit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
of 200 bit/s, and receives on 401.65 MHz at 400 bit/s. The data rate
Data rate
Data rate can refer to:* Bit rate, or data transfer rate* Data signaling rate* Data rate units-See also:* Baud rate* Channel capacity* Throughput* Bandwidth everything in this page is falsified...
is 880 kbit/s at a quantization level
Quantization (signal processing)
Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set – such as rounding values to some unit of precision. A device or algorithmic function that performs quantization is called a quantizer. The error introduced by...
of 12 bits.
Missions
POLDER was first launched as a passenger instrument aboard ADEOS IADEOS I
ADEOS I was an Earth observation satellite launched by NASDA in 1996. The mission's Japanese name, Midori, means "green"....
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
ADEOS II
ADEOS II was an Earth observation satellite launched by NASDA, NASA and CNES in December 2002. Its Japanese name was Midori 2, and it was the successor to the 1996 mission ADEOS I...
. 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
PARASOL (satellite)
PARASOL is a French-built Earth observing research satellite. It carries an instrument called POLDER which studies the radiative and microphysical properties of clouds and aerosols....
microsatellite. Although the satellite has been manoeuvred out of the A-Train on 2 December 2009, data is still being acquired by the satellite.