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A. Roncat, W. Wagner, T. Melzer, A. Ullrich:
"Echo Detection and Localization in Full-Waveform Airborne Laser Scanner Data using the Averaged Square Difference Function Estimator";
The Photogrammetric Journal of Finland, 21 (2008), 1; 62 - 75.

Full-waveform airborne laser scanners (ALS) transmit short laser pulses towards the Earth's surface and record the complete backscattered echo. The backscattered echo from flat terrain is simply a replica of the original laser pulse, but over vegetated and built-up areas the backscattered echo is often rather complex. The waveform is commonly modelled as a superposition of a number of distinct echoes, which involves the detection and localization of these echoes and a non-linear optimization of the model. This paper discusses the averaged square difference function (ASDF) method for detecting and localizing echoes in full-waveform ALS data. The ASDF is analytically equivalent to the direct correlation method. The results of echo detection and range estimation by ASDF were compared empirically with those derived by classical pulse detection in combination with Gaussian Decomposition. Furthermore, the ASDF approach was also tested for its adequacy to suppress false echoes caused by the so-called ringing effect which may occur in ALS data in case of strong echoes. It is found that the results of the ASDF approach coincide to a high percentage with those of Gaussian Decomposition. Moreover, this approach suppresses the detection of false echoes due to the ringing effect.