At the writing of this report, 22 flights have already been mosaicked. Twelve of these flights covers Cebu, eight for Bohol and the remaining and the remaining two for Negros Oriental. In mosaicking flights, the horizontal and vertical shifts or discrepancies are being analyzed. The horizontal shifts are observed on built-up areas to ensure that the elevation has not changed with the difference in flight dates. The vertical shifts consider the average difference in elevation along the overlap of the flights. These values are either added or subtracted to the DEM.
Table 2 2 Sifting values used for mosaicking LiDAR DEM
Figures 2-9, 2-10 and 2-11 presents the mosaicked LiDAR flights for Cebu, Bohol and Negros, respectively.
Extraction of features in the floodplain of riverbasins is done to assess the possible effect of disasters. Features extracted from DSM and orthophoto are buildings, water bodies, roads and bridges.
Features for Kotkot and Mananga River have already been extracted manually. Attribution or the identification of specific names of bridges, roads, water bodies and buildings have not yet been completed. Buildings will also be classified into residential and commercial in attribution.
Figure 2-12 presents an example of the output of extraction of features in Mananga. The shapes outlined in blue are the buildings and the polygons in green are the river shapefiles. The roads and bridges are the described by the black lines.
During the 36th Asian Conference on Remote Sensing (ACRS), which is attended by the our team (ten were able to attend) a paper on feature extraction was presented by our Senior Science Research Specialist, Engr. Bernardo J. Buenaobra. His paper can be found in the appendix.
Calibration of DEM
After mosaicking LiDAR data with different flights, the mosaicked DEM is calibrated. The calibration value is obtained from the calculated difference in elevation of the DEM and the surveyed validation points. Survey of validation points is discussed in the third section. After calibrating, the LiDAR DEM will have elevations referred from mean sea level. Calibrating of DEM covering Inabanga, Abatan and Loboc were done in this year.
The mosaicked Bohol DTMs were not calibrated as the previously available LIDAR DTM was already calibrated by UPD-DPPC. Validation points however were obtained during the survey to countercheck the elevation of the DTM. In the first year, the DTM covering Kotkot and Mananga rivers were already calibrated with a value of 3.54 subtracted from the DTM.
After calibrating the DTM, bathymetric data can be integrated to the rivers. The bathymetric data will describe the elevation beneath the water surface that was not covered by LiDAR. For year 2, bathymetric burning of Abatan, Inabanga, and Loboc rivers has been completed.
In Figure 2-14 it can be observed that in using the identify tool there is already a difference in elevation after integrating the bathymetric data. The bathy burned data is the DEM labeled as abtn_bathy.