Abstract
In order to study forests at the global scale, a detailed link budget for a lidar system onboard satellite is presented. It is based on an original approach coupling airborne lidar observations and an end-to-end simulator. The simulator is initialized by airborne lidar measurements performed over temperate and tropical forests on the French territory, representing a wide range of forests ecosystems. Considering two complementary wavelengths of 355 and 1064 nm, the end-to-end simulator computes the performance of spaceborne lidar systems for different orbits. The analysis is based on forest structural (tree top height, quadratic mean canopy height) and optical (forest optical thickness) parameters. Although an ultraviolet lidar appears to be a good candidate for airborne measurements, our results show that the limited energy is not favorable for spaceborne missions with such a wavelength. A near infrared wavelength at 1064 nm is preferable, requiring ~100 mJ laser emitted energy, which is in agreement with current and future spaceborne missions involving a lidar. We find that the signal-to-noise ratio at the ground level to extract both the structural and optical parameters of forests must be larger than 10. Hence, considering the presence of clouds and aerosols in the atmosphere and assuming a stationary forest, a good detection probability of 99% can be reached when 4 or 5 satellite revisits are considered for a lidar system onboard the ISS or ICESat, respectively. This concerns ~90% of forest covers observed from the lidar, which have an optical thickness less than 3.
Highlights
Forests are key components of surface-atmosphere interactions as demonstrated by previous studies [1,2,3,4,5]
As it was found that 10 m is not enough for ground echo detections (70% probability) through dense forests (FOT > 3), the footprint diameter has to be set to a larger value, which will be a compromise between the probability to detect the ground, the horizontal sampling density of lidar footprints, and the signal-to-noise ratio (SNR)
A value of forest optical thickness (FOT) is associated with each single lidar profile; if FOT ≤ 2TOTmax the probability of good detections depends on the probability distribution of τ, F(τ)
Summary
Forests are key components of surface-atmosphere interactions as demonstrated by previous studies [1,2,3,4,5]. Spaceborne observation, including passive and active remote sensing systems, is a good approach to get such information of canopy structures. Passive multispectral and hyper-spectral sensors produce two-dimensional atmosphere/ground information, whereas their ability to represent 3D spatial patterns is limited Their use for tropical dense forests is not adequate because the remote sensor has difficulty to penetrate the upper canopy layer [17]. A detailed link budget for a canopy lidar system onboard satellite is presented It complements the previously published works [21,22], by using an original approach coupling airborne lidar observations and an end-to-end simulator. The atmospheric scattering properties and the orbital configuration are considered in our numerical simulations
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