Aerial imaging

Posted on December 17, 2021 by Dom

Cost-effective environmental imaging services combining camera drone and cloud technology

As a drone pilot and operator registered with CAA in the UK I’m able to offer a variety of commercial services in open countryside locations, where a full PfCO is not required.

Mapping

On one privately owned site in the Surrey Hills AONB I mapped 32 hectares (79 acres) of part ancient, mixed broadleaf woodland.

Thousands of individual images were stitched together to create an orthomosaic, which was then exported as individual GeoTIFF tiles compatible with GIS software. Very high resolution single images can also be generated (2cm/pixel).

Mapping missions were flown at different times of year to observe seasonal variation.

Analysis

Spectral analysis techniques allow aerial imagery to be used for environmental monitoring at landscape scale. The image below compares visual spectrum vs. enhanced NDVI processing to study plant health.

Visual spectrum vs. NDVI showing replanted woodland

Change detection

Orthomosaic images facilitate accurate measurement to inform effective land management. The aerial map below quickly measured the extent of a heathland fire at Thursley Common NNR in Surrey for Natural England.

Aerial drone map showing extent of Thursley NNR heath fire

Monitoring

Below is an aerial survey of a Homes England residential development at the point where a new access road crosses a river valley intended to form a ‘green corridor’ for wildlife. Orthomosaic, NDVI and elevation visualisations are compared.

This short animation shows the image resolution (~2cm/pixel) attained from the same drone survey mission flown at an altitude of 100m.

Timelapse

By layering orthomosaic images created in different seasons it’s possible to create a wide area timelapse sequence, as shown below.

Video

More conventionally, the video below shows scenes from a Bluebell wood in early spring. Bluebells are an attractive ancient woodland indicator species.

Drone vs. satellite

Drones and satellites offer complementary technologies for aerial imaging, but camera drones enjoy a few advantages:

Resolution
Satellites cannot compete with drones for detail. Satellite images will allow you to see individual trees, but with a drone it’s possible to distinguish each leaf.
Perspective
Satellites are restricted to flat overhead perspectives. A well-operated drone can film or photograph any subject from almost any angle. This can assist in the capture of digital elevation models using 3D point clouds.
Urgency
You don’t need to wait for cloud cover to clear before flying a drone survey! If clouds obscure your satellite image you have no option but to schedule another attempt… and cross your fingers.

Toads on roads

Posted on March 4, 2021 by Dom

Common toad (Bufo bufo) crossing a road at night on migration to breeding pond. Sussex, UK.

After emerging from hibernation in early spring common toads (Bufo bufo) migrate back to their breeding ponds at night. Sometimes this involves crossing busy roads and many toads are sadly hit and killed by passing cars.

Each year volunteers working with charities such as Froglife and local Amphibian and Reptile Groups attempt to ferry migrating toads, frogs and newts to safety at known crossing points.

Common toad (Bufo bufo) juvenile recovered at road crossing on spring migration. Surrey, UK.

Male toads grasp females in a position known as ‘amplexus’ as they attempt to fertilise her eggs. Often a mating pair can be found together before they reach the nearest pond. When this happens males hitch a free ride!

Common toads in amplexus while crossing a road on spring migration

Purbeck mason wasp

Posted on April 18, 2020 by Dom

In the UK the rare Purbeck mason wasp (Pseudepipona herrichii) is found only in the Isle of Purbeck, Dorset.

The female excavates a nest burrow in bare ground on heathland and later seals it with moistened clay.

Purbeck mason wasp (Pseudepipona herrichii) excavating nest burrow on heathland. Dorset, UK.

She stocks her burrow with the larvae of a small moth which feeds mainly on bell heather.

Purbeck mason wasp (Pseudepipona herrichii) with Acleris hyemana moth larva prey at nest burrow entrance. Dorset, UK.

The adults chew distinctive holes in the heather flowers to obtain nectar which their short tongues could not otherwise reach.

Purbeck mason wasp male nectaring on bell heather. Dorset, UK.

The Purbeck mason wasp is thought to rely solely on the larvae of Acleris hyemna, but in 2017 I photographed this female provisioning her nest with what appears to be the moth Acleris notana.

Purbeck mason wasp (Pseudepipona herrichii) with moth larva prey (Acleris notana?) at nest burrow entrance. Dorset, UK.

One small victory for citizen science?

Butterfly Conservation

Posted on December 5, 2018 by Dom

Advancing conservation science through public engagement on digital platforms

Working for the Dorset branch of Butterfly Conservation I developed an online system to document sightings of butterflies submitted by members of the public. This ‘citizen science’ project encourages engagement in nature conservation and adds to our knowledge of these important environmental indicator species.

Since 2014 this recording system has gathered more than 429,000 individual butterfly sightings, contributing to our understanding of these beautiful creatures and the changing world we inhabit.

429,000 individual butterfly sightings

Capture

Butterfly spotters are directed to a web form which collects personal info, location details including grid reference, and species observed.

Butterfly recording form: recorder info
Butterfly recording form: site details

This information is then inserted into the Dorset Branch web sightings database.

Verify

Local experts are given password-protected access to a record management interface on the branch website. Recently submitted butterfly sightings can be reviewed and verified with a single click.

Questionable records can be studied in more detail and individuals contacted to clarify information as necessary.

Interpret

Verified records are instantly published to the branch website, using a number of graphical representations for easy interpretation.

Butterfly data: map
Butterfly data: tree chart
Butterfly data: calendar
Butterfly data: bar chart
Butterfly data: pie chart
Butterfly data: Gantt chart

Drone mapping

Posted on September 4, 2018 by Dom

Experiment in environmental monitoring using a small consumer drone

For a few months now I’ve been experimenting with the use of a small camera drone for environmental monitoring. The quality of the resulting images and the unique perspective it offers have been pleasantly surprising. Its potential applications at relatively low cost are impressive I think.

Red Hill Henge

The site of this Scheduled Ancient Monument lies east of the A3 in Surrey and just north of Junction 10 on the M25 motorway.

‘Making the countryside pay’

In late 2017 Surrey County Council, in collaboration with Surrey Wildlife Trust, decided that this Site of Special Scientific Interest (SSSI) would be a suitable venue to pilot their commercial felling operations in the county.

A licence issued by the Forestry Commission permitted them to extract 30% on 2 occasions over a 10 year period. Upon visiting the site however the impact at ground level looked far more extensive than I would have expected.

Stacks of felled timber — Felling operations on Wisley & Ockham Commons SSSI

Concerned that contractors may have exceeded their remit and damaged the Scheduled Ancient Monument in the process I mapped an area to the north of the site, flying the drone in parallel lines at a height of 60 metres with the downward-facing camera set to take pictures at intervals every few seconds.

Cloud view

With the help of DroneDeploy’s internet cloud software I then stitched the resulting 139 overlapping images together to create an orthomosaic map layer.

Drone map — Area mapped by drone at Red Hill Henge in Surrey.

Orthomosaic map imagery — Orthomosaic detail from drone imagery at Red Hill Henge.

Tracks left by the contractor’s heavy machinery can be seen running across the circular ‘henge-like’ earth bank feature.

Switching to the Normalised Difference Vegetation Index (NDVI) imagery analysis clearly shows the difference between live green vegetation and felled woodland.

NDVI map — Normalised Difference Vegetation Index (NDVI) analysis of felled woodland.

Extra dimension

To help peopIe unfamiliar with the site to visualise the monument in context I then generated a 3D model from the visual point data using DroneDeploy’s online competitor, Pix4D.

3D model of ancient monument — 3D model of Red Hill Henge generated from drone imagery.

For terrain features and dense canopy this technique works well, but it struggles to accurately represent isolated trees and finer features. Without resorting to an expensive aerial LiDAR platform it would be difficult to achieve better results however.

Bright Spark

The little drone done good on this occasion, and with minimal disturbance to this historically and environmentally sensitive site ironically.

Amphibian Kama Sutra

Posted on March 21, 2014 by Dom

Common toads (Bufo bufo) spawning

After emerging from hibernation in early spring, toads migrate back to their breeding ponds.

Males fight to secure mates and often outnumber the females at some sites. When this happens the female may be grasped by several males in a position known as ‘amplexus’, as they compete to be in the best position to fertilise her eggs.

Group of toads in amplexus

Spawning might look fun but can also be life-threatening!

Toad sex is apparently a moveable feast!

The common toad is widespread in Surrey, however populations appear to be declining. Where toad migration routes cross busy roads there can be many fatalities, and local conservation groups police ‘Toad Crossings’ at dusk to help them safely across.

This toad was late to the party, but managed to avoid oncoming traffic

Harvest Mouse Survey

Posted on November 3, 2013 by Dom

Harvest mouse (Micromys minutus) captured on survey after dark

Last week I joined Surrey Wildlife Trust on a harvest mouse survey in wetland habitat beside the River Wey.

Harvest mice are tiny rodents 5cm in length. Their remarkable prehensile tails add an extra 6cm. They live in long tussocky grassland, reedbeds, hedgerows and around woodland edges, building a spherical nest of tightly woven grass, high up amongst the stems. We found several examples at this site:

Harvest mouse nests are woven from a mixture of living and cut grasses which provides excellent camouflage

Nests are the most obvious sign of harvest mouse activity since the animals are especially active around dawn and dusk and rarely spotted in the thick vegetation.

Dozens of rodent-friendly traps of different designs were set in the thick wetland reeds and grasses. Surrey Wildlife Trust staff and volunteers returned three times each day over the course of a week – at dawn, midday and dusk – to ensure that no trapped animals were left for any longer than necessary.

Rodent trap baited with peanut butter, bird seed and dried blowfly larvae

After retrieval from the trap harvest mice are transferred to a transparent bag for weighing and sexing:

Harvest mouse recovered from trap

Harvest mice weigh only 5g on average

Once the details of each rodent have been recorded a small patch of fur is trimmed to identify any animals which are subsequently re-captured.

Marking harvest mouse – a delicate operation!

The highest number of individuals captured was 12 one morning, making this the most abundant site for harvest mice in the county at present.

Harvest mice require very careful handling by trained experts

With thanks to Surrey Wildlife Trust staff and volunteers.

Buglife: Glow Worm Survey

Posted on May 13, 2013 by Dom

Buglife are using my image in their postcard campaign to publicise a glow worm survey in Scotland this summer:

Scottish Glow Worm Survey postcard

Glow worms are widely distributed in the UK, with records from the south of England up to the north of Scotland, but there have been very few Scottish records in recent years.

Butterfly Conservation Moth Report

Posted on February 10, 2013 by Dom

Butterfly Conservation: Moth Report 2013

Butterfly Conservation used my image of a nocturnal moth trapping event to illustrate their latest report:

The State of Britain’s Larger Moths 2013

Unsurprisingly the report concludes that UK moth numbers are in decline, documenting a 40% drop in total abundance in the south of England over the last 40 years.

On the bright side many more moth species have colonised Britain in recent decades than have become extinct.

This photograph was taken at a recent moth trapping event on Chatley Heath organised by Surrey Wildlife Trust. The original image below:

Skinner Trap on Surrey heathland at night

Suburban Oak

Posted on February 6, 2013 by Dom

The ancient Crouch Oak in Addlestone, Surrey, UK

The Crouch Oak once marked the perimeter of Windsor Great Park and is thought to date from the 11th Century, making it in excess of 900 years old.

This ancient tree now looks a little incongruous as a modern residential estate has grown up around it.

The Crouch Oak at night with passing traffic

It’s interesting to compare depictions of this tree from the 19th Century and in 1904 as wooden fences are replaced with metal railings and a dusty track becomes a surfaced road. The oak also enjoyed an additional limb in those days.

In more recent times the Crouch Oak survived an arson attempt in 2007 and is now fitted with metal grilles across its hollow openings to prevent a repeat.

Metal grille stops burning objects being thrown inside

To see the Crouch Oak for yourself follow the map below to the bend in Crouch Oak Lane:

Dom Greves Digital / Blog

Digital media production & wildlife photography in Dorset and Surrey

Category Archives: Conservation

Aerial imaging

Mapping

Analysis

Change detection

Monitoring

Timelapse

Video

Drone vs. satellite

Toads on roads

Related links

Purbeck mason wasp

Related links

Butterfly Conservation

Capture

Verify

Interpret

Archive

Share

Coordinate

Drone mapping

Red Hill Henge

‘Making the countryside pay’

Cloud view

Extra dimension

Bright Spark

Amphibian Kama Sutra

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Harvest Mouse Survey

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Buglife: Glow Worm Survey

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Butterfly Conservation Moth Report

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Suburban Oak

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Mapping

Analysis

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Timelapse

Video

Drone vs. satellite

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Capture

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Red Hill Henge

‘Making the countryside pay’

Cloud view

Extra dimension

Bright Spark

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