Our Services

BNG Baseline Survey.
RICS-regulated aerial input for Biodiversity Net Gain.

UAV LiDAR canopy height, multispectral orthomosaic and measurable habitat base mapping — the aerial-survey layer underneath the ecology consultant's UKHab v2 baseline assessment. Signed accuracy report on every deliverable, audit-trail-ready for the responsible body and the statutory metric.

Band D/E
RICS hard-detail accuracy
2–5 cm
Orthomosaic GSD
±25 cm
Canopy height accuracy
Request a Quote How it fits the BNG workflow
What it is

What is a BNG baseline survey?

A Biodiversity Net Gain (BNG) baseline survey is the on-site evidence pack that records the habitat type, distinctiveness, condition and area present on a development site before any works begin. Under the mandatory BNG regime in England (Environment Act 2021, commencement February 2024), the baseline is the reference state against which the 10 % net gain is calculated using the statutory metric.

An ecology consultant compiles the assessment. The underlying survey inputs — habitat polygons, canopy heights, condition photographs — must be measurable, dated and traceable to a recognised survey standard. That is the layer Angell Surveys provides.

Angell Surveys is a RICS-regulated practice (Firm 681790). UAV operations conducted under the appropriate CAA authorisations.

How it fits

What does a BNG baseline aerial survey contribute that an ecologist's walkover does not?

Three things a field walk cannot produce: a measurable habitat base map from an orthomosaic dated and georeferenced to OSGB36, on which polygon boundaries are drawn at survey-grade accuracy; a LiDAR canopy height model that separates woodland, scrub and grassland strata across the whole site rather than at sample points; and a signed accuracy report that gives the statutory metric an auditable measurement trail. We capture; the ecologist classifies.

StepWhoWhatOutput
1. Site captureAngell Surveys (Chartered)UAV LiDAR + multispectral orthomosaic, dated GNSS-controlledClassified point cloud, DTM, DSM, CHM, orthomosaic, signed accuracy report
2. Habitat polygon delineationAngell Surveys / Ecologist (joint)Boundary polygons drawn over the orthomosaic at survey-grade accuracyGeoPackage / Shapefile of habitat parcels
3. UKHab v2 classificationQualified EcologistHabitat type + distinctiveness + strategic significance per parcelUKHab v2 attributed dataset
4. Condition assessmentQualified EcologistField walk recording condition criteria per parcelCondition-attributed habitat polygons
5. Statutory metricQualified EcologistHabitat units (and hedgerow / watercourse units) calculated and post-development scenario assessedStatutory metric calculator + baseline report
6. Periodic monitoringAngell Surveys (Chartered)Year 5/10/15/20/25/30 re-survey, same flight plan + GCPsChange-detection layer + epoch-to-epoch accuracy report
The pack

What you receive.

Every BNG baseline aerial-survey engagement delivers the same evidence pack — designed to drop straight into the ecology consultant's report and stand up to verifier scrutiny.

  • Classified point cloud — LAS / LAZ (ASPRS classification: ground, low / mid / high vegetation, built, noise).
  • Bare-earth Digital Terrain Model (DTM) — GeoTIFF, 25–50 cm grid.
  • Digital Surface Model (DSM) — GeoTIFF, 25–50 cm grid.
  • Canopy Height Model (CHM = DSM − DTM) — the primary activity-data layer for woodland and scrub classification.
  • Multispectral orthomosaic — GeoTIFF, 2–5 cm GSD, dated and georeferenced to OSGB36 / OSTN15.
  • Habitat polygon dataset — GeoPackage / Shapefile, drawn at survey-grade boundary accuracy.
  • Signed accuracy report (PDF) — RMSE + maximum residual at independent check points, RICS Band statement, signed by Philip M. Angell MRICS.
  • Methodology statement (PDF) — capture parameters, flight plan, GCP layout, processing software and quality assurance trail.
  • Optional: permanent control markers — steel pins in concrete, GNSS-fixed, for repeatable epoch-to-epoch re-survey over the 30-year BNG monitoring window.
Authority

Published methodology.

The methodology behind this service is documented in BNG Habitat Baselines — a published practitioner's brief in the Aerial Surveying Briefs series by Philip M. Angell MRICS (2026, Kindle & Paperback).

The companion brief sets out the chartered-surveyor approach to baseline capture, habitat polygon delineation, monitoring discipline and the audit trail that survives challenge at planning committee and biodiversity-gain-site verification.

For ecology consultants and BNG developers commissioning baseline assessments, the brief is a useful pre-read — it makes clear which work sits with the chartered surveyor and which with the qualified ecologist, and the audit-trail structure both professions share.

Available on Amazon (Philip M. Angell author page) alongside Aerial Surveying: A Practitioner's Guide, AI for Chartered Professionals and the rest of the Aerial Surveying Briefs series.

Scope

Where this method has limits.

An aerial BNG baseline gives the ecologist a measurable, dated habitat map; it does not replace the ecologist.

Condition and species

Habitat condition, species presence and distinctiveness are assessed on the ground by the ecologist; the aerial data maps extents and structure to support that assessment.

Season

Habitat boundaries and canopy structure vary with season; capture timing is agreed with the ecologist and recorded.

Vegetation height

Tree and hedgerow heights come from LiDAR or photogrammetric surface models with stated uncertainty; small or understorey features may not be resolved.

The metric

Statutory biodiversity metric calculations remain the ecologist's responsibility; our deliverable is the evidenced geometry behind them.

Angell Surveys delivers this service across the UK from a London base, under RICS regulation, with the same documented control, check-point verification and QA on every project. Accuracy is specified and reported against the band table in RICS Measured Surveys of Land, Buildings and Utilities, 3rd edition (RICS, 2014), using independent check points rather than a marketing figure.

FAQs

Frequently asked questions.

What is a BNG baseline survey?
A Biodiversity Net Gain (BNG) baseline survey is the on-site evidence pack that records the habitat type, distinctiveness, condition and area present on a development site before any works begin. Under the mandatory BNG regime in England (Environment Act 2021, commencement February 2024), the baseline is the reference state against which the 10% net gain is calculated using the statutory metric. An ecology consultant compiles the assessment; the underlying survey inputs — habitat polygons, canopy heights, condition photographs — must be measurable, dated and traceable to a recognised survey standard. That is the layer Angell Surveys provides.
Where does an aerial survey fit in the BNG workflow?
Aerial survey gives the ecology consultant three things their field walk cannot: a measurable orthomosaic at 2–5 cm GSD for habitat polygon delineation, a LiDAR canopy height model that classifies vegetation strata without sample bias, and a contemporary, dated base map that the verifier can independently audit. We capture; the ecologist classifies. The clear professional split — RICS-regulated surveyor for measurement, qualified ecologist for habitat condition assessment — is the audit-trail structure UKHab v2 and the statutory metric expect.
How accurate does a BNG baseline need to be?
The statutory metric drives commercial value at the hectare level, but boundary disputes between habitat polygons are decided at the metre level — and challenged at the centimetre level if a small parcel changes distinctiveness category. UAV photogrammetric capture delivers ±10–25 mm absolute positional accuracy on hard detail at 1σ (RICS Band D/E), which exceeds anything achievable from desk-based aerial imagery and removes the boundary-ambiguity problem entirely. Canopy heights from UAV LiDAR are reported to ±25 cm at canopy top.
Are you ecology consultants?
No — and that is the point. Angell Surveys provides the RICS-regulated aerial survey, the measurable base data and the signed accuracy report. The ecology consultant retains professional responsibility for the habitat classification, UKHab v2 mapping, condition assessment and statutory metric calculation. The two professional credentials together — chartered surveyor for measurement, qualified ecologist for ecological judgement — produce a baseline that survives planning challenge and biodiversity-gain-site verification.
What about post-development monitoring?
BNG units must be maintained for 30 years and monitored throughout. The same UAV capture methodology applied to the baseline becomes the activity-data layer for periodic re-survey — typically year 5, 10, 15, 20, 25, 30. Year-on-year comparison against the dated baseline orthomosaic and canopy height model gives the responsible body objective evidence of habitat condition trajectory. This long-tail monitoring contract is where the survey relationship pays back.
Are you RICS regulated?
Yes. Angell Surveys is regulated by the Royal Institution of Chartered Surveyors (RICS) — verify our registration at ricsfirms.com/office/681790/Angell-Surveys-Ltd. Every BNG aerial-survey deliverable is signed by Philip M. Angell MRICS; Angell Surveys is regulated by RICS. The signed accuracy report is what makes the survey evidence auditable by the responsible body, the planning authority and any subsequent challenger.
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BNG Baseline Enquiry

Commissioning a BNG baseline assessment? We can scope the aerial-survey component within one business day.

Most scoping responses sent within one business day.

RICS-regulated work, led by Philip M. Angell MRICS.

Discuss your BNG Baseline Survey Call 020 4652 4948