Hydro International | Year: 2013
The evolution of multi-beam echo sounders (MBES) is leading to systems with enhanced capabilities in their traditional markets, but also provides features to allow the expansion of their use into new areas and applications. The quest for higher quality systems is primarily realised by increases in system resolution. These advances are largely achieved by producing systems of smaller beamwidths and reduced pulse lengths. Thus, it is now quite common to find systems with half-degree beamwidths, and beams of 0.3 and 0.4 degrees are available. These specifications are to be found in systems catering for the shallowwater markets, which operate in the higher frequency range. Naturally, there is a trade-off between frequency and range. In order to achieve the highest resolution, a high frequency is necessary but useable range will then be compromised. Manufacturers are overcoming range limitations by introducing a frequency modulated (FM) sweep, in addition to the traditional continuous wave (CW) pulse.
Colditz R.R.,Geomatics |
Acosta-Velazquez J.,Colegio de Mexico |
Diaz Gallegos J.R.,University of Arts and Science of Chiapas |
De Vazquez Lule A.,Geomatics |
And 4 more authors.
International Journal of Remote Sensing | Year: 2012
Change detection is one of the primary applications of remote-sensing data, and many techniques have been developed during the past three decades. Although frequently criticized and despite many alternatives, due to its simplicity and intuitive manner, post-classification change detection still remains one of the most applied techniques. Many studies in the field of change detection analysis acknowledge, for instance, the impact of misregistration, inconsistencies in classification schemes or differences in methods for image interpretation. However, there are additional, rarely studied influences that can cause large errors in change detection results, including integrating multi-resolution data, the adjacency effect and the minimum mapping units (MMUs) that are applied to the classification before change detection. This study demonstrates these effects for the complex land cover of the Alvarado mangrove area at the Mexican Gulf Coast, employing 10 m Système Pour l'Observation de la Terre 5 (SPOT-5) high geometric resolution (HRG)-based and 57 m Landsat Multispectral Scanner (MSS) classifications. As a baseline, the proportion of the fine spatial resolution classes within the coarse spatial resolution cells were derived, from which proportional change matrices were computed. The analysis employs difference measures to compare change matrices and proportional maps. The impact of various tested resampling functions was negligible if coarse resolution data were refined. For coarsening fine spatial resolution data, change matrix comparison was comparatively small but yielded differences of approximately 20% in spatially explicit measures. Incorrect positional alignment indicated differences of up to 5% in the change matrix for a misregistration of 100 m and even higher spatially explicit differences (28%). The discrepancies due to the adjacency effect were rather low. MMUs of 25 ha resulted in differences of up to 36% in the change matrix. The magnitude of the discrepancies of all studied effects depends on the class diversity in the map, and some can also be related to the difference in spatial resolution. © 2012 Copyright Taylor and Francis Group, LLC.