Bathymetry Study of the Siltation Level of Lugu Dam Reservoir in Sokoto State, Nigeria

This paper seeks to determine the siltation level of the Lugu dam reservoir, Sokoto State, Nigeria, using the bathymetric survey method. A total of eleven (11) ground control points were established over the study area using Hi-Target Global Navigation Satellite (GNS) Real-time Kinematic (RTK) System. The base station was set- up over the reference Bench Mark while the Rover station was moved around to predetermine locations of the ground control points. The depths to the Lugu dam reservoir bed, as well as its underwater topographic mapping with a section of the River Rima on the right flank of the reservoir area, across the collapsed spillway were conducted using Garmin Global Positioning System Map. This was mounted on a nine feet fibre boat to enhance the echo sounding. The result of the study was used to produce a digital elevation model, topographic contours and the area-elevation-capacity curve for the reservoir. This indicates that between elevations 260.5 m and 262 m, the available minimum and maximum designed storage capacities of Lugu dam reservoir ranges from 21.24 MCM and 34.25 MCM respectively. The Lugu dam reservoir maximum storage capacity at breached level stands at 25 MCM, while its active storage capacity is 20 MCM. This is to conclude that the amount of siltation at the reservoir is 9.25 MCM representing 27.01% indicating the difference between the maximum designed capacity and the current storage capacity. It is recommended that dredging be carried out to regain the initial designed storage capacity as this will no doubt put an end to the incessant flooding and erosion experienced in the area.

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Spatial Accuracy of UAV-Derived Orthoimagery and Topography: Comparing Photogrammetric Models Processed with Direct Geo-Referencing and Ground Control Points

GEOMATICA ◽

10.5623/cig2016-102 ◽

2016 ◽

Vol 70 (1) ◽

pp. 21-30 ◽

Cited By ~ 41

Author(s):

Chris Hugenholtz ◽

Owen Brown ◽

Jordan Walker ◽

Thomas Barchyn ◽

Paul Nesbit ◽

...

Keyword(s):

Satellite System ◽

Base Station ◽

Measurement Unit ◽

Ground Control ◽

Lower Grade ◽

Control Points ◽

Gps Receiver ◽

Spatial Accuracy ◽

Ground Control Points ◽

Mean Square Errors

Mapping with unmanned aerial vehicles (UAVs) typically involves the deployment of ground control points (GCPs) to georeference the images and topographic model. An alternative approach is direct geo ref er encing, whereby the onboard Global Navigation Satellite System (GNSS) and inertial measurement unit are used without GCPs to locate and orient the data. This study compares the spatial accuracy of these approaches using two nearly identical UAVs. The onboard GNSS is the one difference between them, as one vehicle uses a survey-grade GNSS/RTK receiver (RTK UAV), while the other uses a lower-grade GPS receiver (non-RTK UAV). Field testing was performed at a gravel pit, with all ground measurements and aerial sur vey ing completed on the same day. Three sets of orthoimages and DSMs were produced for comparing spa tial accuracies: two sets were created by direct georeferencing images from the RTK UAV and non-RTK UAV and one set was created by using GCPs during the external orientation of the non-RTK UAV images. Spatial accuracy was determined from the horizontal (X,Y) and vertical (Z) residuals and root-mean-square-errors (RMSE) relative to 17 horizontal and 180 vertical check points measured with a GNSS/RTK base station and rover. For the two direct georeferencing datasets, the horizontal and vertical accuracy improved substantially with the survey-grade GNSS/RTK receiver onboard the RTK UAV, effectively reducing the RMSE values in X, Y and Z by 1 to 2 orders of magnitude compared to the lower grade GPS receiver onboard the non-RTK UAV. Importantly, the horizontal accuracy of the RTK UAV data processed via direct georeferencing was equivalent to the horizontal accuracy of the non-RTK UAV data processed with GCPs, but the vertical error of the DSM from the RTK UAV data was 2 to 3 times greater than the DSM from the non-RTK data with GCPs. Overall, results suggest that direct georeferencing with the RTK UAV can achieve horizontal accuracy comparable to that obtained with a network of GCPs, but for topographic meas urements requiring the highest achievable accuracy, researchers and practitioners should use GCPs.

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Evaluation of the Georeferencing Accuracy of a Photogrammetric Model Using a Quadrocopter with Onboard GNSS RTK

Sensors ◽

10.3390/s20082318 ◽

2020 ◽

Vol 20 (8) ◽

pp. 2318 ◽

Cited By ~ 5

Author(s):

Martin Štroner ◽

Rudolf Urban ◽

Tomáš Reindl ◽

Jan Seidl ◽

Josef Brouček

Keyword(s):

Vertical Component ◽

Satellite System ◽

Bundle Adjustment ◽

Ground Control ◽

Control Points ◽

Ground Sample ◽

Ground Control Points ◽

Aerial Vehicle ◽

Global Navigation Satellite ◽

Orientation Parameters

Using a GNSS RTK (Global Navigation Satellite System Real Time Kinematic) -equipped unmanned aerial vehicle (UAV) could greatly simplify the construction of highly accurate digital models through SfM (Structure from Motion) photogrammetry, possibly even avoiding the need for ground control points (GCPs). As previous studies on this topic were mostly performed using fixed-wing UAVs, this study aimed to investigate the results achievable by a quadrocopter (DJI Phantom 4 RTK). Three image acquisition flights were performed for two sites of a different character (urban and rural) along with three calculation variants for each flight: georeferencing using ground-surveyed GCPs only, onboard GNSS RTK only, and a combination thereof. The combined and GNSS RTK methods provided the best results (at the expected level of accuracy of 1–2 GSD (Ground Sample Distance)) for both the vertical and horizontal components. The horizontal positioning was also accurate when georeferencing directly based on the onboard GNSS RTK; the vertical component, however, can be (especially where the terrain is difficult for SfM evaluation) burdened with relatively high systematic errors. This problem was caused by the incorrect identification of the interior orientation parameters calculated, as is customary for non-metric cameras, together with bundle adjustment. This problem could be resolved by using a small number of GCPs (at least one) or quality camera pre-calibration.

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DIRECT GEOREFERENCING ON SMALL UNMANNED AERIAL PLATFORMS FOR IMPROVED RELIABILITY AND ACCURACY OF MAPPING WITHOUT THE NEED FOR GROUND CONTROL POINTS

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprsarchives-xl-1-w4-397-2015 ◽

2015 ◽

Vol XL-1/W4 ◽

pp. 397-402 ◽

Cited By ~ 26

Author(s):

O. Mian ◽

J. Lutes ◽

G. Lipa ◽

J. J. Hutton ◽

E. Gavelle ◽

...

Keyword(s):

Base Station ◽

Test Area ◽

Rural Setting ◽

Inertial System ◽

Ground Control ◽

Control Points ◽

Post Processing ◽

Ground Sample ◽

Ground Control Points ◽

Test Flight

This paper presents results from a Direct Mapping Solution (DMS) comprised of an Applanix APX-15 UAV GNSS-Inertial system integrated with a Sony a7R camera to produce highly accurate ortho-rectified imagery without Ground Control Points on a Microdrones md4-1000 platform. A 55 millimeter Nikkor f/1.8 lens was mounted on the Sony a7R and the camera was then focused and calibrated terrestrially using the Applanix camera calibration facility, and then integrated with the APX-15 UAV GNSS-Inertial system using a custom mount specifically designed for UAV applications. <br><br> In July 2015, Applanix and Avyon carried out a test flight of this system. The goal of the test flight was to assess the performance of DMS APX-15 UAV direct georeferencing system on the md4-1000. The area mapped during the test was a 250 x 300 meter block in a rural setting in Ontario, Canada. Several ground control points are distributed within the test area. The test included 8 North-South lines and 1 cross strip flown at 80 meters AGL, resulting in a ~1 centimeter Ground Sample Distance (GSD). <br><br> Map products were generated from the test flight using Direct Georeferencing, and then compared for accuracy against the known positions of ground control points in the test area. The GNSS-Inertial data collected by the APX-15 UAV was post-processed in Single Base mode, using a base station located in the project area via POSPac UAV. The base-station’s position was precisely determined by processing a 12-hour session using the CSRS-PPP Post Processing service. The ground control points were surveyed in using differential GNSS post-processing techniques with respect to the base-station.

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THEORETICAL ANALYSIS OF POSITIONAL UNCERTAINTY IN DIRECT GEOREFERENCING

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xli-b1-1221-2016 ◽

2016 ◽

Vol XLI-B1 ◽

pp. 1221-1226

Author(s):

Ali Coskun Kiraci ◽

Gonul Toz

Keyword(s):

Graphical User Interface ◽

Inertial Navigation System ◽

Satellite System ◽

Ground Control ◽

Control Points ◽

Positional Uncertainty ◽

Ground Control Points ◽

Field Works ◽

Global Navigation Satellite ◽

Orientation Parameters

GNSS/INS system composed of Global Navigation Satellite System and Inertial Navigation System together can provide orientation parameters directly by the observations collected during the flight. Thus orientation parameters can be obtained by GNSS/INS integration process without any need for aero triangulation after the flight. In general, positional uncertainty can be estimated with known coordinates of Ground Control Points (GCP) which require field works such as marker construction and GNSS measurement leading additional cost to the project. Here the question arises what should be the theoretical uncertainty of point coordinates depending on the uncertainties of orientation parameters. In this study the contribution of each orientation parameter on positional uncertainty is examined and theoretical positional uncertainty is computed without GCP measurement for direct georeferencing using a graphical user interface developed in MATLAB.

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Performance of UAV-Based Digital Orthophoto Generation for Emergency Response Applications

TEM Journal ◽

10.18421/tem104-31 ◽

2021 ◽

pp. 1721-1727

Author(s):

Burak Akpınar

Keyword(s):

Emergency Response ◽

Satellite System ◽

Ground Control ◽

Control Points ◽

Earthquake Hazards ◽

Emergency Situations ◽

Ground Control Points ◽

Digital Orthophoto ◽

Global Navigation Satellite ◽

Gnss Observations

Unmanned Aerial Vehicles (UAVs) have been used for accurate orthophoto generation based on advanced Global Navigation Satellite System (GNSS) techniques. In recent years, the UAV systems have become an effective tool for fast monitoring of damages caused by disasters such as the earthquake hazards. The conventional orthophoto generation based on ground control points takes too much time during emergency situations. In the study, different methodologies for the processing of the acquired GNSS Positioning data for direct georeferencing of UAVs were investigated in terms of various orbit products. Evaluating the fitness for emergency response applications, the ground control points (GCPs) also used for validation of the generated orthophoto without using GCPs and based on Precise Point Positioning (PPP) approach. In this study, Ultra-Rapid, Rapid and Final PPP methods based on GNSS observations were used for direct geo-referencing. Thirteen GCPs were located at the study area for the validation of the orthophoto accuracy generated by direct geo-referencing.

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