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water depth can be computed as the difference of the water surface peak and the seabed peak. The maximum depth 
which can be reached in this way is limited by the water turbidity, and is measured in terms of the so called Secchi depth. 
This indicator is defined as the maximum depth at which the human eye is able to detect a specific circular disk with a 
diameter of 30 cm in the water. 
ALB was developed in the 1960s with the primary goal of finding submarines. Hickman and Hogg [3] proposed to use 
ALB for bathymetric survey. In the 1970s some ALB prototypes were successfully developed and tested [4]. In recent 
years this technique has become increasingly important due to improved hardware and better processing software. This 
development has also made possible the recording of the waveform of the backscattered signal [5]. In [6], a seabed map 
of sand and seagrass was produced using both the corrected waveform and underwater video data recorded during the 
flight campaign. Moreover, the classification of the ALB data was studied using inherent characteristics of the recorded 
waveforms [7, 8]. Pe’eri et al. [9] investigated ALB-based land-water interface algorithms with green-, red-, and infrared 
channel waveforms to detect the shoreline of rocks, vegetation and man-made features. As a further application ALB was 
applied to map submerged archaeological structures over large areas in high detail. The results showed that the technique 
is mature enough to be utilized for underwater heritage management [10]. In combination with side-scan sonar, 
shipwrecks were indentified and their dimensions could be measured [11]. Recently, full-waveform processing 
algorithms for single-wavelength ALB were investigated for a better extraction of seabed points [12, 13]. 
3. DATA ACQUISITION 
3.1 Study area 
To investigate the applicability of ALB monitoring for the German Baltic Sea Coast, three flight campaigns were 
performed close to the island of Poel in the German Baltic Sea. The test areas were of varying size with slightly different 
locations. In order to carry out a comparison under equal conditions, we focus only on the overlapping area of the three 
flight campaigns, which is 95.8 km 2 in size. The location of the study area is shown in Figure 1. Most parts are covered 
by water, but the area also comprises some small shore regions. Concerning the water depth a variation can be observed 
from 0 m to the maximum depth of 23.2 m. This value is deeper than the expected depth which is currently reached by 
ALB sensors under the available turbidity level; in fact it was chosen to determine the limitation of the penetration depth. 
Figure 1. Overview of the study area, which is highlighted by the yellow boundary. 
3.2 Flight campaigns 
The first data set was acquired by Milan Geoservice GmbH, Germany, with a Riegl VQ-820-G Sensor in the beginning 
of November 2012. This sensor works with a green laser (/. = 5.32 nm) solely. In the investigated overlapping area, 
25 strips with an overlap of 70% were acquired. For this survey the pulse repetition rate was set to 149 kHz. The flying 
height was 500 m above ground level. A first quantitative analysis of the ALB data near the island of Poel was reported 
in [14, 15]. The second data set was collected by TopScan GmbH, Germany, in the end of September 2013 with 
Proc. of SPIE Voi. 9638 96380Z-2