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Low Altitude Remote Sensing Of Compact Sites
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Low Altitude Remote Sensing Of Compact Sites (LARSOCS)

 

Funded by: 

• L-Universita’ ta’ Malta

• Research, Innovation, Development Trust Fund (RIDT) small project grant

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LARSOCS is an interdisciplinary project selected for funding by the Research, Innovation and Development Trust fund (RIDT) in 2016. The project, which formally started on the 1st of October 2016, has included staff from the Faculty of Arts, Faculty of Engineering and Institute of Earth Science, together with a contributor from Italy and one French and one Maltese intern. 

The aim of LARSOCS was to create a low-cost capability for low altitude aerial remote sensing and survey for archaeology, which can also be used for other areas of research including geosciences, environment, resource and cultural heritage, and this was achieved. A capability for remote sensing over small sites using an off-the-shelf system flown at altitudes below 50m created and is already expanding beyond the original paramters. The feasibility and usefulness of taking images at altitudes of 5m or less above ground level has been proven; the creation of a dedicated drone system controlled by a Local Positioning System, has been partially achieved, and the development of the system is in progress. This activity will proceed to its termination after the formal end of the LARSOCS project duration in September alongside other derivative activities. 


PROJECT TEAM

Dr Ing. John C. Betts (coordinator) - Department of Classics and Archaeolgy (Faculty of Arts)

Dr Maxine Anastasi - Department of Classics and Archaeolgy (Faculty of Arts)

Dr Charles Galdies - Institute of Earth Systems

Dr Gianmarco Alberti

Dr Ing. Marc Anthony Azzopardi – Dept of Electronics Systems Engineering (Faculty of Engineering)

Dr Ing. Brian Zammit - Dept of Electronics Systems Engineering (Faculty of Engineering)

Ms Mannaïg L’Haridon – Masters student, French National School of Geomatics (E.N.S.G.), Paris

Mr Karl Galea

Mr Nicky Patiniott 

 

UAVs 

FIG1 

The DJI Phantom 3 Advanced UAV starting a survey flight at Żejtun on 24th July 2017. 

 

 fig2

 DJI Mavic UAV

 

PROJECT FLIGHTS

February to June 2017: Quarrying area adjacent to Clapham Junction, Dingli - flights at 5 m, 10 m, 20 m above ground; nadir and oblique

July 2017: Punic-Roman site, Żejtun – flights at 2-3 m, 5 m, 10 m

August 2017: Cart ruts, Clapham Junction, and Ghar il-Kbir, Dingli – flights at 10 m


OUTCOMES 

Clapham Junction quarry site

The flights at the quarry areas near Clapham Junction were used for training in the use of the DJI Phantom 3 Advanced. Nadir-pointing photos were taken over Roman period quarrying areas, and an orthophoto and DEM were produced.  

fIG3 

3D model of quarrying area at the west end of the Clapham Junction archaeological site, Dingli. Model by Gianmarco Alberti.

 

FIG4 

A Digital Elevation Model (DEM) created using 130 azimuthal (vertical down) shots. The dense point cloud created in the Agisoft PhotscanPro software featured about 30,000,000 points generated using a high-quality setting. The DEM resolution is 1.3 cm/pixel. DEM by Gianmarco Alberti

 

fig5 

Identification of terrain features using photogrammetry-derived DEM and Local Relief Modelling. Top-left: overview of the DEM – the red rectangle represents the analysed area; top-right: hillshaded image derived from the DEM; bottom: hillshaded image with LRM raster superimposed - red and blue colours highlight peaks and troughs. The inset profile graph indicates that, across the section represented by the solid black line, the negative linear features are about 1.5 and 2.0 cm deep. DEM and LRM by Gianmarco Alberti

 

Click here to view the flight over the quarry area capture video imagery. This is useful for documenting sites and producing display material, but single shots of better quality were preferred to extraction of screenshots from videos.  

 

Zejtun Punic/Roman site

Low level flights were carried out over the Punic/Roman site in which fieldwork has been carried out by the Department of Classics and Archaeology annually since 2006. The aims in this instance was to verify capability for recording images at very low level above ground, down to 2 m height; and to record the fieldwork carried out in July 2017.  

fig6 

Image taken from 10 m height above ground over area A (left half of photo) and surroundings. The red and white divisions on the scale bars close to the centre of the image and at top left are 20 cm each. The upper scale bar is resting on the tiled domestic area, and just below (or North) of it are a pair of vine trenches, an excavated one to the left and an unexcavated one to its right. Most of the features in the left half of the image were backfilled with stones or soil to ensure their conservation, and are currently no longer visible, highlighting the importance of these images as a record of the site and fieldwork.

 

fig7 

Image taken from 2.5 m height above ground over area C. This is a detail from the upper right of fig. 11 showing a water channel, the width of the channel being around 13 cm. The smallest stones which can be distinguished are less than 1 cm in size.

 

An orthomosaic (see below) was produced from images taken at 10 m above ground. The mosaic recorded the state of the site at the end of the 2017 fieldwork, and will be useful in supporting the interpretation of the stratigraphy of the site by providing a visual reference to the detail drawings and textual records which are the basis of the stratigraphic record. 

fig8 

Orthophoto by Mannaig L’Haridon

 

Clapham Junction Cart Ruts

Flights were also carried out over Clapham Junction cart ruts. The intention is to compile a series of photos covering the entire Clapham Junction area to produce a record of the site. Litchi flight planning and control was used to guide the DJI Phantom 3 Advanced UAV and to generate photos with sufficient overlap to generate a photomosaic. 

fig9 

Screenshot of Litchi mission hub showing one of the flight plans used at Clapham Junction. The total distance flown at the chosen speed at 20 m above ground is 662 m, the duration of flight 8 minutes. The camera was set to take a photo every five seconds. Prepared by Mannaig L’Haridon using Litchi software.

 

fig10 

One of the several photos taken over the west end of the Clapham Junction cart rut site.

 

fig11 

DEM and Local Relief Modelling of Clapham Junction cart ruts. The main image shows a DEM of the area, the inset is a 3D visualization of the area in the black rectangle. The model is based on a set of shots; the dense point cloud features about 40,000,000 points and model resolution is 1.50 cm/pixel. DEM and LRM by Dr Gianmarco Alberti 

 

Local Positioning System (LPS)

The UAVs used have onboard GPS receivers which are used for flight control and which provide the location of images taken. The accuracy is of an order of magnitude of a few metres. Whilst this is not an issue when flying at altitude, when the instantaneous field of view of a photograph has sides of the order of tens of metres, it becomes significant at very low level, when the side of the field of view is much smaller. The GPS error became significant, and although the drone is flown in as near a straight and regular path as possible, retaining the correct degree if overlap (60% – 70%) between subsequent photos and subsequent parallel and adjacent flight lines is not easy as in this case the GPS was of little or no help in keeping the drone close to its intended position. Use of a LPS would resolve this issue, although it is clear that an efficient and effective feedback system is required to ensure the required degree of positional control. As part of the LARSOCS project this system is currently being developed at the Department of Electronics Systems Engineering, and will be tested for flights carried out at 2 m above ground level.  

 

FUTURE WORK

LARSOCS will proceed beyond its original planned one year span, and will include the following activities: 

• Continuation of development of the LPS

• Use of the drone for photographing Clapham Junction cart ruts and quarries

• Flights over other archaeological areas

• Support of Department fieldwork and student projects

• Support of a project currently under development for providing persons with visual impairment with more access to archaeological site interpretation

• Development of an alternative control system together with the Department of Systems and Control, Faculty of Engineering

The UAVs will also be available for other projects and student activities, and undergraduate and postgraduate students are encouraged to develop projects which use this equipment. The Department is also open to collaboration on projects in this area of UAV use with local or international partners. 

 

 LINKS

Links to 3D models produced by Dr Gianmarco Alberti from LARSOCS photos.



 

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Last Updated: 26 October 2017

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