The Parasol mission was designed to fulfil specific science objectives: studying clouds and aerosols in Earth’s atmosphere and describing their radiative and microphysical properties. To do this, Parasol took advantage of all the data provided by several sensors on the Aqua platform, Calipso and CloudSat.
Greenhouse gases have long been the sole focus when studying the causes of global warming. But scientists building climate models and studying the Earth’s net radiation, such as the French Laboratoire de météorologie dynamique (dynamic meteorology laboratory, LMD) have shown that natural and man-made aerosols play a key role in climate change. According to the French Academy of Science, they could even represent “the biggest source of uncertainty when calculating radiative forcing.”
The Parasol mission was approved in 1999 and aimed to take polarised reflectance multi-directional measurements, prioritising areas which were observed by the Calipso satellite’s LIDAR. Radiation from the Sun is not polarised until it travels through certain particles like aerosols, water droplets or ice crystals. Parasol measured polarised light in multiple directions in order to better understand clouds and aerosols by observing different characteristic than the typical spectral signature.
Parasol provided more accurate data on the quantity and size distribution of aerosols found above oceans, as well as on their turbidity above land masses, in order to evaluate radiative forcing from sunlight. Furthermore, the project helped in detecting clouds, determining their thermodynamic state and their altitude, and estimating the amount of sunlight reflected by cloud cover. It also helped assessing the integrated water vapour content.
Parasol’s objectives were to describe the radiative properties of clouds and aerosols by taking advantage of the combined data provided by its own instruments and those from the other A-train satellites. These include Aqua’s Ceres and Modis radiometers, Calipso’s LIDAR and CloudSat’s radar.
The Aqua, Calipso and CloudSat missions’ primary objective is to provide an estimation of our planet’s net radiation by taking measurements in different spectral ranges (optical and micro-wave) observable from space and by combining wide-field and focused measurements.
In this context, the Parasol mission aimed to take polarised albedo multi-directional measurements, first and foremost on areas which have been observed by Calipso’s LIDAR.
This coordination with the Aqua, Calipso, and CloudSat missions introduced 3 major requirements for the Parasol operations:
- The orbit parameters, set as follows:
- an altitude of 705 km,
- an inclination of 98.21° (Aqua) or 98.08° (Calipso),
- an equator flyover local time compatible with those of Aqua (1.30 pm) and Calipso (2.10 pm at the beginning of the mission, and 12.50 pm by the end).
- The launch date, set during the other satellites’ active phase.
- Necessary cooperation between the mission centres for each satellite when it came to orbit control or data processing.