In the first half of 2010 ATIAIA ENERGY hired ESTEIO to carry out topobathymetric surveys over Sucuriú river in the city of Costa Rica -MS, to enable the basic project for the construction of the Hydroelectric Power Plant of Fundãozinho. For this service, ESTEIO executed 10 topobathymetric sections and an aerophotogrammetric flight using LIDAR technology, in order to determine digital terrain model (DTM) and digital surface model (DSM), generating contour lines until quota 502 meters. There was also the location of contour line 500 meters on the ground and profile line survey along the river. The services were implemented according to technical specifications of ANEEL (Brazilian Electricity Regulatory Agency).
PLANNING
The activities of this service began with the recognition of planimetric and altimetric benchmarks of IBGE (brazilian geodetic authority) availlable in the region, as well as the evaluation of their conservation status. Since existing benchmarks were chosen, we started planning to install and measure new geodesic benchmarks within the boundaries of the work area, as well as to choose a benchmark to be used as base station to LIDAR flight.
TOPOBATHYMETRIC SURVEYS
Various RRNN (altimetric benchmarks) were used as reference for transferring elevation. Along the line 06 geodetic benchmarks were implanted and their respective azimuth marks, which served as reference to locate topobathymetric sections and contour line 500 m. The beginning and ending points of each section were also leveled. The closure error of leveling lines was better than 8 mm √k.
To bring horizontal coordinates to the benchmarks within the work area a polygonal was conducted, started and finished in 02 different points SAT, which error of closure equal to 1: 535,000. This polygonal adjustment for errors distribution included all new horizontal benchmarks and their azimuths.
The topobathymetric sections were performed with total stations, since most sections were in forested area, disabling the use of RTK GPS.
LIDAR FLIGHT
In order to determine contour lines with equidistance of 01 meter ATIAIA opted for the use of LIDAR technology. The service was designed so that it had sufficient points density for determining the contours, properly setting parameters such as field of view (FOV), aircraft altitude and lateral overlap, allowing to obtain cloud of points with density of 3.3 dots / m².
20 flight tracks were programmed to cover the 28.94 km² hired.
The existence of a large flat area located upstream of the dam and with little altimetry variation made it difficult to perform field leveling works, the definition of this area was only possible by LIDAR technology, which allowed a better definition of contours.
DTM AND DSM
DTM classification was conducted automatically with TerraScan software, based on classification parameters varied according to terrain slope. Non ground points were separated taking into account geometric distribution, altitude and laser pulse return intensity.
DTM classification was conducted automatically with TerraScan software, based on classification parameters varied according to terrain slope. Non ground points were separated taking into account geometric distribution, altitude and laser pulse return intensity.
DSM (Digital Surface Model) was obtained after filtration of points which are not part of the surface. This process was automated to optimize time and errors that would occur in a manual process.
The points that were part of this product were all returns (all points) measured in profiling.
CONTOURS
DTM points, already filtered and purified form the “cloud” of LASER points referring to the ground. These points were treated with TIN type algorithms (Triangle Irregular Network) to form triangles and consequently create contour lines.Contours generating algorithms have various processing filters, from providing smoothing to contours, improving their appearance, to “small islands” elimination (closed contours). Automatic editing parameters were tested and adjusted to the characteristics of the work area.
CONTROL POINTS
In addition to topographic points, checkpoints for LASER survey were scheduled for evaluation and control of the products.
These points were evenly distributed throughout the area and arranged at locations in the overlapping area of laser strips and along them, they should also offer good conditions for GNSS surveying. 12 control points were used, referenced to geodesic benchmark SAT 93 559, which also served as GNSS base station during the LIDAR flight.To improve confidence in the overall result and provide homogenization of field points with laser data, points of topobathymetric sections were used to control the laser altimetry.
These points, obtained by leveling, served to generate geoid correction in the cloud of laser points
291 points distributed evenly in the area were measured. The final topographic statistical result was:
SHEETS INDEX
In order to become viable and to standardize the generation of contracted products, the area of 28.94 km² was divided into 140 sheets. The sheets are homogeneous and continuous, as well as their nomenclature, following the numerical sequence from number 001 to number 140. Each sheet has approximately 0.27 square kilometers in area.
Due to relief differences in the area, each sheet has a different altimetry range, so there is no radiometric connection between the sheets, also each sheet will have its respective legend (key).
PRODUCTS