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Entwicklung und Erprobung eines abbildenden Laseraltimeters für den Flugeinsatz unter Verwendung des Mehrfrequenz- Phasenvergleichsverfahrens / C. Hug (1996)

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Titre :	Entwicklung und Erprobung eines abbildenden Laseraltimeters für den Flugeinsatz unter Verwendung des Mehrfrequenz- Phasenvergleichsverfahrens
Titre original :	[Élaboration et expérimentation d'un altimètre laser pour l'intervention en vol en utilisant des procédés multifréquence-phases différentes]
Type de document :	Thèse/HDR
Auteurs :	C. Hug, Auteur
Editeur :	Munich : Bayerische Akademie der Wissenschaften
Année de publication :	1996
Collection :	DGK - C
Sous-collection :	Dissertationen num. 457
Importance :	122 p.
Format :	21 x 30 cm
ISBN/ISSN/EAN :	978-3-7696-9500-7
Note générale :	Bibliographie
Langues :	Allemand (ger)
Descripteur :	[Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] altimètre laser [Termes IGN] faisceau laser [Termes IGN] lasergrammétrie [Termes IGN] phase [Termes IGN] télémètre laser aéroporté [Termes IGN] télémétrie laser aéroporté
Index. décimale :	35.10 Acquisition d'images
Résumé :	(Auteur)This paper investigates the usefulness of the principle of multi-frequency sidetone ranging for three-dimensional airborne terrain survey. The potential and the limits for scanning laser altimeters using this ranging scheme are discussed. An experimental setup is described, which was realised to study the behaviour of the ranging principle under real-world conditions. The results of laboratory and flight tests are presented and evaluated. In sidetone ranging, the distance between the sensor and a target is determined by measuring the phases shift of sinus-oidal signals (sidetones) modulating a continuous laser beam, after having been reflected by a remote surface. Range measurements with a very high resolution can readily be realised this way at high measurement rates. Multiple frequen-cies are used to provide a large unambiguous range. Due to the high resolution and accuracy potential, of this ranging method, it seemed a promising idea to implement it into an airborne sensor for 3-D terrain survey. A highly collimated monoscopic ranging beam combined with the high sampling rates and the high range resolutions allow 3-D surface mapping in great detail. Additionally, surface reflectance can easily be derived from the sidetone amplitudes in the return signal, which are independent of foreign illumination. An experimental scanning laser altimeter setup suitable for airborne tests was realised. Its key components are a laser diode, which is amplitude modulated by two sidetone frequencies, and a rotating mirror which deflects the ranging beam conically at 10 Hz. Range and reflectance are sampled at 7.5 kHz. At an altitude of 500 m above ground, the surface is sampled within a swath of 170 m with a sample point diameter of 0.5 m, and distances between neighbouring samples are 0.8 m across the direction of flight and at most 6 m along track. The maximum range was found to be 570 m with a range resolution between 0.03 m and 0.17 m . These values correspond well to values predicted by model calcu-lations. The characteristic behaviour of the ranging scheme under real-world conditions was studied by comparing the data col-lected by the laser altimeter during a test flight, with a reference digital elevation model (DEM) generated from stcreophotogrammetrically evaluated aerial photos. The mean altitude difference between both data sets is 0.23 m with a standard deviation of 0.5 m. Significant altitude differences can only be observed at the edges of buildings and above vegetation. A detailed analysis reveals that the majority of deviations results from shadows in the aerial photos, causing no-data areas in the reference DEM. and occasional sensor misbehaviour at surface discontinuities. The multi-frequency sidetone ranging scheme performed especially well in detecting continuous surface modulation with high accuracy. Also, the shapes and sizes of natural and artificial surface objects were captured precisely. Surprisingly, even in forested areas, ground and canopy points were discriminated well. The tests, however, also showed, that ranging to water surfaces is not possible. The combination of reflectance and elevation data turned out be useful to automatically distinguish between artificial and natural surface objects (e.g. houses and trees). In conclusion, multi-frequency sidetone ranging can be considered well suited as a powerful ranging scheme for high-resolution scanning laser altimeters. It was successfully implemented in a functional sensor which, although experimen-tal, already proved competitive with commercial laser rangers of the same class, which operate on the pulse-time-of-flight ranging principle. In addition, the realised scanning laser altimeter co-registers surface reflectance simultaneously to range, which opens the field for new methods of automatic surface object classification.
Numéro de notice :	28022
Affiliation des auteurs :	non IGN
Thématique :	IMAGERIE
Nature :	Thèse étrangère
Permalink :	https://documentation.ensg.eu/index.php?lvl=notice_display&id=63369

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
28022-01	35.10	Livre	Centre de documentation	En réserve M-103	Disponible
28022-02	35.10	Livre	Centre de documentation	En réserve M-103	Disponible

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