Combining single photon and multispectral airborne laser scanning for land cover classification

Feasibility of using single photon lidar (SPL) data for land cover classification was studied for the first time. Data from the Espoonlahti suburban study area in Finland were acquired with the SPL100 sensor from a flying altitude of 3600 m above ground level and classified into six classes using an object-based, random forest classification approach. The overall accuracy was 66% compared with a set of reference points. The results were good for buildings and trees, but there was significant confusion between ground-level land cover classes. The possibility to enhance classification accuracy by combining SPL data with multispectral intensity information from airborne laser scanning (ALS) was also tested and led to an overall accuracy of 86%. The multispectral intensity image was obtained by combining intensity data from two channels of the Optech Titan multispectral ALS sensor (infrared and near-infrared) with the SPL intensity (green). To allow for comparisons between SPL and conventional linear-mode ALS, single-channel data from the Optech Titan (near-infrared) were also applied for the same classification task. In this case, the overall accuracy was 83%. An important factor affecting the lower quality of the SPL results was the rough appearance of the intensity images created from the SPL data. Despite high point density, small features such as narrow roads were often difficult to distinguish in the intensity images. This relates to the SPL technique and preprocessing operations applied to the data. Considering future use of new ALS datasets, the different benefits of different systems need to be taken into account. A clear benefit of the SPL technique is its high efficiency in data acquisition. SPL is seemingly fit for deriving high objects that are distinguishable by using geometric rather than intensity information. The classification accuracy of buildings and trees was comparable in each classification test, although the flying altitude of the SPL100 was five times that of the Optech Titan. We propose that raw echo waveforms would be provided together with point cloud data to allow users to create their own intensity and echo width features usable for classification purposes. Combining multispectral intensity with SPL, in reference to multispectral single photon lidar, could result in a technique that is effective for mapping large areas and will also allow for automated classification of ground-level objects in a more reliable manner.