Assessing global aerosol profiles
Aerosols are tiny particles suspended in Earth’s atmosphere that wield significant influence over the global climate. They interact with solar radiation and are key to the formation of clouds. These miniscule particles come from a range of natural and man-made sources, such as deserts and industry. This variability in origin, as well as in time and space, poses a significant challenge to scientists who want to monitor and characterise aerosols. “Aerosol particles are therefore one of the main sources of uncertainties in climate projections,” explains Daniel Perez-Ramirez, researcher in the Applied Physics Department at the University of Granada and GRASP-ACE project coordinator. In the EU-funded GRASP-ACE project, researchers aimed to reduce the uncertainties surrounding these particles, developing an open-source code able to combine measurements of aerosols from various space-borne instruments. This includes light detection and ranging (LIDAR) – a relatively new technology that uses lasers to measure objects.
Open-source code for remote sensing
Generalized Retrieval of Atmospheric and Surface Properties (GRASP) is an open-source code capable of combining different remote sensing measurements sensitive to the optical properties of aerosols and surfaces. GRASP has been used successfully in the past, but the advent of space-based LIDAR opens up new possibilities. This active remote sensing technique can characterise the atmosphere vertically through the use of pulsed lasers and advanced electronic detection. However, LIDAR has limitations for deriving microphysical properties of the atmosphere, particularly of aerosols.
Multi- to single-wavelength LIDAR identifies aerosol microphysical properties
The GRASP-ACE project, carried out with the support of the Marie Skłodowska-Curie Actions programme, fully investigated the possibility of obtaining aerosol microphysical properties by multi-wavelength LIDAR measurements alone. “We found that a priori constraints about aerosol types must be applied, which limited the potential to fully characterise aerosol globally,” notes Perez-Ramirez. “Moreover, multiwavelength LIDAR measurements are very complex and expensive, which limits them for obtaining extended data sets,” he adds. The GRASP-ACE team therefore explored the use of single-wavelength LIDAR in combination with passive remote sensing such as polarimetry (a measurement of the polarisation of sunlight) for space measurements, and sun photometry (a measurement of sunlight) for ground measurements. “When using LIDAR measurements in GRASP, and combined with other passive remote sensing measurements, it is possible to obtain these vertically resolved aerosol microphysical properties,” notes Perez-Ramirez. As single-wavelength LIDAR is considerably easier and its cost much cheaper, this will bring down the cost of future space missions analysing aerosols.
New possibilities in aerosol measurement
“The great achievement of our project is the possibility of combining space LIDAR and polarimetry measurements to obtain vertically resolved aerosol properties, which has not been possible yet,” explains Perez-Ramirez. “Particularly important will be the possibility of characterising aerosol size distribution and absorption properties,” he adds. After the promising results of the project, a new EU-funded project, GRASP-SYNERGY, has been approved. The aim will be to combine information from different space sensors using the GRASP algorithm. The research will support an upcoming Atmosphere Observing System (AOS) space mission led by NASA in cooperation with other space agencies, planned for 2029. The GRASP algorithm offers a way to reduce the costs of this mission, by incorporating information from the cheaper single-wavelength LIDAR. ”The mission architecture includes the combination of LIDAR and polarimetry, thus making GRASP a core part for optimisation and mission success,” says Perez-Ramirez.
Keywords
GRASP-ACE, aerosol, climate, clouds, size, distribution, origin, sensors, LIDAR, NASA, code
