What is the range of accuracies for airborne lidar measurements of land topography and water bathymetry? Assume no vegetation cover on land and low turbidity of water!
LIDARs penetrates to about 5/beam-attenuation coefficient in water. This sets an upper threshold on the depth. WRT accuracy: That depends on the temporal response of your receiver. If you can resolve signals delat_c apart, you will be able to have an accuracy on the order of light speed in water x delta_t. Given that the signal is strongly attenuated in water, typically the receiver will integrate over a significant delta_t. Remember that the speed of light in water is 30% slower than in air, hence with a similar system you will get 30% less accuracy in water compared to land. For more, see e.g. http://ccom.unh.edu/theme/lidar and reference therein.
Emmanuel,
After penetrating 5/beam attenuation coefficient, the lidar beam gets attenuated further on its way back to the detector. So what is the useful depth for lidar applications to bathymetry? Some authors say it is 3 times the Secchi depth.
Emmanuel,
I guess the 5/beam attenuation coefficient distance includes total pulse travel distance down and up, right?
5/beam attenuation is compared to the total depth. One could argue that this value should be system (that is detector) dependent.
Victor, I believe that the real depth, from which a remote sensor "see", depends on underwater light field (e.g., a degree of turbidity or attenuation coefficient) and accuracy that you wish to get. Recently, me & Yosef Yacobi published a paper on this issue: https://www.researchgate.net/publication/51735155_Comparison_of_chlorophyll_a_concentration_detected_by_remote_sensors_and_other_chlorophyll_indices_in_inhomogeneous_turbid_waters?ev=prf_pub Maybe, this paper and references there will help you...
Article Comparison of chlorophyll a concentration detected by remote...
Bathymetric measurement is absolutely dependent on the water turbidity.
I quizzed the reps from Airborne Hydrography at Oceanology last year and they were claiming 15 cm vertical resolution and 50 cm horizontal.
Penetration up to 50 m in really clear water (i.e. a Caribbean study) and much lower in turbid waters.
Their website is here and my be useful:
Experiences from the airborne laser scanning for creation of a national DEM for Sweden have shown that it is possible to achieve heigh uncertainty of below 0.1 m on planar hardtop surfaces (e.g. asphalt).
Victor,
In the airborne laser bathymetry data that I worked with the depth penetration was roughly 2.5 times the sechi dish depth in very clear coastal waters. The data were collected by the airborne SHOALS bathymetry system in 1999 and 2000 operated by the Corps of Eng for our coral reefs study area in Hawaii. The approximate max water depth in those very clear waters was 45m or so and had a vertical resolution of 15cm. We overlaid the bathy data on top of digitized aerial images and combined it with some shipborne dual-frequency acoustic data. The bathy data were very high quality and we were able to basically treat it like a DEM on land (i.e., compute slope, aspect, and spatial variability values/images). Attached are 3 slides showing you an example of the data set and derivative image products (I hope the attachment worked ok).
Pat
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