José Luis Pérez

Analysis of Landslide Evolution Affecting Olive Groves Using UAV and Photogrammetric Techniques

This paper deals with the application of Unmanned Aerial Vehicles (UAV) techniques and high resolution photogrammetry to study the evolution of a landslide affecting olive groves. The last decade has seen an extensive use of UAV, a technology in clear progression in many environmental applications like landslide research. The methodology starts with the execution of UAV flights to acquire very high resolution images, which are oriented and georeferenced by means of aerial triangulation, bundle block adjustment and Structure from Motion (SfM) techniques, using ground control points (GCPs) as well as points transferred between flights. After Digital Surface Models (DSMs) and orthophotographs were obtained, both differential models and displacements at DSM check points between campaigns were calculated. Vertical and horizontal displacements in the range of a few decimeters to several meters were respectively measured. Finally, as the landslide occurred in an olive grove which presents a regular pattern, a semi-automatic approach to identifying and determining horizontal displacements between olive tree centroids was also developed. In conclusion, the study shows that landslide monitoring can be carried out with the required accuracy—in the order of 0.10 to 0.15 m—by means of the combination of non-invasive techniques such as UAV, photogrammetry and geographic information system (GIS).

A New Two-Step Robust Surface Matching Approach for Three-Dimensional Georeferencing of Historical Digital Elevation Models

In this letter, a new approach based on a two-step (coarse and fine) automatic surface matching for registering two overlapping multidate digital elevation models (DEMs) is proposed to avoid the costly and time-consuming ground-control-point acquisition. The proposed methodology was tested to georeference a historical grid DEM obtained from a photogrammetric flight taken in 1977 and located at a heavily developed coastal area of Almería (southeast Spain). The reference DEM consisted of a newer DEM produced by the Andalusia Regional Government from a photogrammetric flight taken in 2001. The results obtained from this work may be deemed as very promising, showing high efficiency and accuracy for historical-DEM georeferencing. The vertical accuracy of the finally coregistered DEM was computed over a recent LiDAR-derived DEM (validation data set) which presented relatively unaltered areas, yielding a standard deviation that is fairly similar to the estimated uncertainty of the reference DEM.

Methodology for Landslide Susceptibility and Hazard Mapping Using GIS and SDI

In this work a methodology for preparing landslides susceptibility and hazard maps is presented, based in a bivariate analysis between past movements and determinant factors. The methodology for determining the susceptibility is an adaptation of the matrix method to a GIS, and it has been tested and validated in different zones and environments of Andalusia (southern Spain). The text also discusses the availability of information layers in Spanish SDI to developing these susceptibility maps. For the hazard evaluation, we propose a methodology of determining the susceptibility in different return periods from inventories of landslides that show activity in these considered periods. The activity was estimated from stereoscopic and monoscopic analysis of aerial photographs from different dates, using geological and geomorphic criteria, and the study of rainfall time series. Since all, four periods were considered in a logarithmic scale of 10 years (approximate return period of rainfall generating instability in the area), 100, 1000 and 10000 years. After determining the susceptibility, it was transformed into annual hazard dividing by the number of years of the return period. Finally, a total hazard map was obtained by determining at each point the maximum value of hazard of the different periods and it is expressed in several intervals.

Efficient methods to convert LiDAR-derived ellipsoid heights to orthometric heights

Abstract Nowadays cartographic products are usually obtained from data sources which provide large amount of data. LiDAR acquisition system is a good example of the great quantity of data obtained, such as points with spatial coordinates in a determined reference system. The height of these points is usually related to a global ellipsoid (e.g. WGS84), but the local vertical reference system, and so the corresponding orthometric heights, are usually measured from a local geoid which is adjusted for a country or region. Orthometric height determination can be performed for each point by knowing the undulation value which relates the ellipsoid to the geoid for each position. However, this operation may not be necessary for all points if we take into account the LiDAR specifications. Thus we can use a simplification which minimizes the processing time for this calculation. In this paper we present the results obtained by applying several simplifications to drastically shorten the number of point-to-point computations to obtain the orthometric height from the raw LiDAR point cloud data.

Evaluacion de macroceldas de corrosion embebidos en vigas de concreto reforzado bajo ambiente salino

In this work, corrosion of reinforcing steel in concrete beams exposed to two environments was evaluated. The two environments used were: drinking water (white) and salt water (5% NaCl sol.) for 18-months. The concrete had a water/cement ratio of 0.40 and 0.60, respectively. Monitoring was carried out by measuring macrocell voltage and current, with open-circuit potentials and electrochemical noise. The results presented more probability of corrosion in beams immersed in salt water with higher water/cement ratios and reaching the system a state of passivation. The macrocells were very useful for analyzing the corrosion system and correlated electrochemical techniques.