SUMO Air Space - Your Questions Answered
- Claire Rose
- May 8, 2024
- 1 min read
Updated: Jun 19, 2024
The latest from SUMO GeoSurveys, providing a range of aerial and geospatial surveys using drones, known commercially as UAS (Unmanned Aircraft Systems).
Ask the Audience!
It is important to us that you are as informed as possible when commissioning a UAS survey to make sure you know exactly what you can get out of it. You can find the answers to some frequently asked questions below…
Q: What is multispectral and how does it work?
In brief, multispectral uses a sensor array which collects images at different wavelengths. These images can be processed to identify the health of plants on the surface. Since plant health can be influenced by sub-surface features, multispectral surveys can show where these features are by the appearance of the plants in the processed image. Therefore, archaeology which doesn’t leave a topographic footprint may still be revealed by UAS multispectral mapping.
Q: What level of accuracy can you achieve with your georeferencing, particularly over large landscapes?
We typically aim for a georeferencing error of <3 cm. On projects which require even tighter accuracy, we can combine our data with a traditional topographic or laser scanning survey.
Q: What solution can you offer for obtaining ground levels beneath tree canopies where photogrammetry cannot reach?
We frequently collaborate with SUMO’s traditional topographic department. Where tree canopies obscure the surface, a terrestrial topographic survey can be used to fill in the gaps.
Q: Is photogrammetry better than LiDAR?
We consider each survey on a case-by-case basis to ensure the best methodology is followed to suit the needs of the job. LiDAR is only preferred over photogrammetry when the survey requires the construction of a Digital Terrain Model (DTM) beneath dense vegetation, in particular woodland. For open sites, such as pastures or urban landscapes, the improved resolution from photogrammetry over LiDAR makes it the preferred choice.
Q: At what hectarage does UAS-based LiDAR become more cost effective than manned LiDAR?
Manned aircraft are significantly more expensive to commission than UAS. In addition, the ground resolution from a UAS at a maximum of 400ft is much better than that of a plane at a 1000ft. Since UAS surveys can cover over a hundred hectares in a day, manned LiDAR is best suited for surveying extensive woodland where ground control is virtually impossible, and resolution is less of a priority.
Q: What are the optimum conditions for a UAS survey?
In order to operate safely, it is important that we carefully consider the weather for every job we carry out. Generally, we aim for days which are dry with low winds and proceed only if it’s practicable to do so. Very often, we only find out what the weather will really be like when we arrive on site.
Each of our survey methods have further nuances to encourage the best results.
RGB photogrammetry works best with little shadow cast over or across the subject; multispectral photogrammetry is most effective within a two hour window either side of midday; thermal building surveys are best carried out at night when there is no solar radiation interference, whereas thermal solar farm inspections require high levels of solar irradiance during the day to be successful.
Q: How quickly can you go from instruction to delivery of results?
Since UAS surveys are dependent on the ever-changing weather forecast, we are very used to attending site with little notice. We always aim to meet specific dates as provided by the client and make contingencies for the weather when necessary. Initial outputs (e.g orthophoto, Digital Elevation Models, and 3D model) can be provided within 1 – 2 days of the survey, and we aim to deliver the interpretive report within 2 – 4 weeks.
Q: Can you operate in restricted airspace?
In short, yes, we can operate in most restricted airspace. Prior to supplying a quote, we check to see what airspace your site falls in as this may have a bearing on when we can carry out the survey. It is a legal requirement, governed by the CAA (Civil Aviation Authority) to ensure that we seek permission to fly in restricted airspace, such as FRZs (Flight Restriction Zones) for airfields, prisons, and military bases. There are few instances where UAS operations are not permissible, however we are aware of these locations and can make alternative arrangements if required.
Q: Can you carry out earthwork surveys for planning conditions?
Absolutely, a photogrammetry survey is the ultimate tool for identifying topographic and micro-topographic features across a site. The outputs include an orthophoto and DEM (Digital Elevation Model), the latter of which can be manipulated in GIS software to analyse the site, and an interpretive report can be drawn up to show the findings.
Q: How familiar with UAS surveys are county archaeologists?
Our services are being increasingly requested by county archaeologists and, as with all our customers, we are always happy to educate them about the benefits of our techniques and outputs.
Q: Can photogrammetry be used in Historic Building Recording instead of traditional photos and annotation?
We greatly recommend using photogrammetry in conjunction with traditional photos for Historic Building Recording to produce thorough reports. External photogrammetry is used to generate scalable orthographic elevations which can aid the production of phase plans, whereas traditional photos are favoured internally. In addition, the photogrammetry survey collates an archive consisting of hundreds of photos, as well as the building being preserved as a 3D model.
Q: Can UAS be used inside buildings, such as churches?
Yes, UAS can be operated inside buildings. We have conducted photogrammetry and general video and photos from within buildings including churches.
Q: What outputs can you provide from a building survey?
Photogrammetry surveys can produce a range of deliverables, depending on the needs of the client. Standard outputs include scaled orthorectified elevations and roof plan, and a link to a low-resolution 3D model for online viewing. Further outputs include a point cloud, high-resolution 3D model files, all survey photographs, general video, and panoramic spheres. In addition, we can combine our outputs with laser scan data as part of a detailed Measured Building Survey.
Q: Is there any archaeology which photogrammetry doesn’t work on?
It’s very unlikely that photogrammetry would struggle to work on archaeology since the general materials and surfaces we tend to find in historic settings – such as masonry, earthworks, landscapes, excavations, and even artefacts – are ideal for photogrammetric modelling.
