Civil Engineering September 2021 | Vol 29 No 8

26 September 2021 Civil Engineering Q Q Drone operation types Q Q Type of drones available Q Q Battery life required for the duration of the bridge inspection Q Q Rotational cameras for under-bridge inspection Q Q High resolution camera cost versus sufficient quality Q Q Influence of limited illumination under a bridge Q Q Image processing software Q Q Ability to identify defects from pro- cessed images. The main objectives for the use of drones and image processing are to: Q Q Improve the inspection methodology Q Q Improve the quality of inspections Q Q Create a safer environment for inspectors. The scope of this paper is to present the results of the initial phase of the study, which presents the proof of concept of drone bridge inspections using image processing to estab- lish if these technologies can be adopted for use in the South African context. Legal Requirements Pertaining to the use of Drones in South Africa When considering the use of drones for bridge inspections, it is important to consider the legal and regulatory require- ments pertaining to drone operations in South Africa. Aviation regulations in South Africa for drone operations remain rela- tively strict compared to other countries. Operating drones in South Africa is subject to the following rules, unless approved by the South African Civil Aviation Authority (SACAA, 2017): 1. Drones may not be flown within a 10 km radius of an airport without spe- cial permission from the South African Civil Aviation Authority (SACAA) 2. Drones with a mass exceeding 7 kg may not be flown 3. Drones may not be flown within 50 m of people or private property (without permission from the property owner) 4. Drone pilots must maintain a visual line of sight with their drones at all times while in flight 5. Drones may only be flown during daylight hours 6. According to the SANPARKS website , “The use of drones inside (or over) national parks is strictly prohibited”. The main limitation for the use of drones for bridge inspections in South Africa is flying within 50 m of a public road. Permission to operate outside the mentioned rules can be granted by the SACAA and should be included in the Remotely Piloted Aircraft Systems (RPAS) Operators Certificate (ROC). Each drone operation requires dif- ferent licences for approval depending on the type of operation. The different licences required for the different types of operation are summarised in Table 1 (Kock, 2015). Using drones for bridge inspections requires a commercial licence and in- cludes the following (SACAA, 2017): Q Q Air service licence Q Q RPAS operator’s certificate Q Q RPAS letter of approval Q Q Remote pilot licence Q Q Certificate of registration Q Q RPAS maintenance technician. The process to obtain approval for a specific operation requires the following six steps (SACAA, 2017): 1. Registration of the drone 2. Letter of approval from the Director of the SACAA 3. Pilot licence 4. Operator’s certificate 5. Submit flight plan detailing the mission 6. Permission from landowner. Methodology For the proof of concept, two bridges were identified from the Gauteng provincial bridge network. TMH 19 visual assessments of these two bridges were conducted in 2016 and the inspection data for both bridges, including all the identified defects, the DER ratings of these defects, the PCI and inspec- tion and inventory photos, are available. The two bridges were chosen based on their proximity to Pretoria and Cullinan and their location on a road with a low traffic volume. The locations of the two bridge structures are shown in Figure 1. The Gauteng Department of Roads and Transport (GDRT) gave permission as landowner for the drone inspections of the two bridges. Staff from the CSIR and an industry partner, Premier Mapping Africa, conducted two visual bridge inspections using drones on 17 February 2020. The drone inspection data captured for the two bridges was processed and point cloud models were created for further analysis. The 2016 bridge inspection data for the two bridges was then used to determine if the same defects could be identified using the point cloud model. Premier Mapping Africa manages aerial survey projects and is licenced to offer aerial survey services using full sized aircraft as well as RPAS (drones). Premier Aviation holds an Air Operator Certificate for manned aerial surveys and an ROC for RPAS aerial photography, surveys and industrial inspections. Overview of the 2016 Visual Bridge Inspection Information Information for the two bridge structures extracted from the GDRT BMS is pro- vided in Table 2. The defects recorded for the two bridges during the 2016 inspection are shown in Table 3. The Railway Bridge is in a fair condition, mainly as a result of the abutment seating cracks. Discussion of the Drone Inspections Images of the two bridges were captured using the DJI Inspire2 drone with a Zenmuse x4S camera mounted on the Table 1 RPAS operations versus required approval Type of operation Required approval Commercial Corporate Non-profit Private Air Service Licence (ASL) YES N/A N/A N/A RPAS Operators Certificate (ROC) YES YES YES N/A RPAS Letter of Approval (RLA) YES YES YES N/A Remote Pilot Licence (RPL) YES YES YES N/A Certificate of Registration (C of R) YES YES YES N/A Table 2 BMS information for the two bridges used in the study Bridge no. Bridge name PCI value Condition category D631_01N_B4435 Railway Bridge 64.3 Fair D631_01N_B4095 Boschkop River Bridge 93.8 Very Good