Polder: the story on HearLore

Polder

The POLDER instrument possessed the unique ability to see the invisible texture of the atmosphere, capturing not just the intensity of light but the very angle at which it bounced off the Earth. Before its launch, scientists could measure how bright the sky was, but they lacked the tools to understand the complex dance of light polarization that revealed the hidden shapes of clouds and aerosols. This passive optical imaging radiometer and polarimeter, developed by the French space agency CNES, transformed the static view of the planet into a dynamic map of atmospheric interactions. It 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. The device did not merely take pictures; it measured the physical properties of light itself to deduce the nature of the objects it observed.

A Push Broom Scanner

The engineering behind POLDER relied on a push broom scanner that swept across the Earth's surface with a precision that defied the limitations of earlier technology. The device's optical system used a telecentric lens and a charge-coupled device matrix with a resolution of 242x548 pixels, creating a detailed mosaic of the planet below. The focal length was set to a specific value to ensure clarity, and the focal ratio of 4.6 allowed for a wide field of view ranging from plus or minus 43 degrees to plus or minus 57 degrees, depending on the tracking method. This mechanical design allowed the instrument to capture data continuously as the satellite moved, painting a picture of the Earth one line at a time. The mass of the instrument was kept low to fit within the constraints of the host satellites, while its power consumption of 77 W in imaging mode ensured it could operate efficiently during critical observation windows.

The Spectrum Of Life

By scanning between 443 and 910 nanometers full width at half maximum, the instrument could distinguish between the deep blues of the ocean and the vibrant greens of the vegetation. The shorter wavelengths between 443 and 565 nanometers typically measured ocean color, allowing scientists to track the health of marine ecosystems and the concentration of phytoplankton. In contrast, the longer wavelengths between 670 and 910 nanometers were used to study vegetation and water vapor content, providing a window into the carbon cycle and the moisture levels in the air. This spectral versatility meant that a single instrument could monitor the health of the oceans, the growth of forests, and the composition of the atmosphere simultaneously. The data transmission occurred at 465.9875 MHz with a bit rate of 200 bit/s, while receiving commands on 401.65 MHz at 400 bit/s, ensuring that the vast amount of information gathered could be sent back to Earth with minimal loss.

What is the POLDER instrument and what does it measure?

The POLDER instrument is a passive optical imaging radiometer and polarimeter developed by the French space agency CNES. It measures the physical properties of light itself to deduce the nature of objects it observes, including solar radiation reflected by Earth's atmosphere, tropospheric aerosols, sea surface reflectance, and the Earth Radiation Budget.

When was the POLDER instrument first launched and when did the mission end?

The POLDER instrument was first launched as a passenger instrument aboard ADEOS I on the 17th of August 1996. The mission ended on the 30th of June 1997 when communication from the host satellite failed, cutting short the data collection period after ten months.

How does the POLDER instrument distinguish between ocean color and vegetation?

The POLDER instrument distinguishes between ocean color and vegetation by scanning between 443 and 910 nanometers full width at half maximum. The shorter wavelengths between 443 and 565 nanometers typically measure ocean color, while the longer wavelengths between 670 and 910 nanometers are used to study vegetation and water vapor content.

What happened to the POLDER 2 mission launched in 2002?

The POLDER 2 mission launched in December 2002 aboard ADEOS II ended prematurely after 10 months when the satellite's solar panel malfunctioned. This failure left the instrument in darkness and unable to power its systems, resulting in the loss of valuable data on long-term atmospheric changes.

When was the third generation POLDER instrument permanently shut down?

The third generation POLDER instrument was permanently shut down on the 18th of December 2013. This decision was made to ensure the safety of the space environment and to prevent the creation of space debris, bringing an end to a mission that had spanned nearly two decades.

Polder

A Push Broom Scanner

The Spectrum Of Life

Common questions

What is the POLDER instrument and what does it measure?

When was the POLDER instrument first launched and when did the mission end?

How does the POLDER instrument distinguish between ocean color and vegetation?

What happened to the POLDER 2 mission launched in 2002?

When was the third generation POLDER instrument permanently shut down?

The First Flight And The Fall

The Second Attempt And The Silence

The Final Orbit And The Shutdown