Before a uranium prospect becomes a drill programme, it often passes through an awkward middle stage.

Regional geophysics may show that an area deserves attention, but the anomaly may still be too broad to decide where first-pass drill lines should go.

Ground radiometric surveying can add detail, but in remote terrain it may expose crews to slow traverses through vegetation, boggy ground, relief, wildlife risk and limited communications.

That is where UAV (Unmanned Aerial Vehicle) radiometrics can play a useful role. It is not a replacement for geological mapping, sampling, drilling, magnetic data, electromagnetic data or structural interpretation. It is a way to sharpen one specific layer of the exploration model: the near-surface distribution of radioelements over selected targets.

Gamma rays

Gamma-ray spectrometry maps radioelement concentrations and has long been used in geological mapping and mineral exploration. In uranium exploration, the relevant channels are typically potassium (K), equivalent uranium (eU) and equivalent thorium (eTh).

The word "equivalent" matters: eU and eTh are inferred from gamma emissions associated with decay products, so uranium-series disequilibrium can affect interpretation if the decay chain has been disturbed.

For that reason, a radiometric anomaly should be treated as exploration evidence, not as an assay, a grade estimate or proof of ore.

The technical value of flying lower and slower is straightforward, but it is sometimes overstated. In gamma-ray surveying, spatial resolution is influenced by flight height, line spacing, ground speed, detector response, source-detector geometry and the contrast between an anomaly and its background.

UAV-based gamma spectrometry can help close the resolution gap between conventional crewed airborne surveys and ground surveys, but only if acquisition geometry, positioning and later geological follow-up are good enough to support interpretation.

A recent Altomaxx Technologies project for a remote uranium exploration client illustrates the point.

The client already had helicopter-based radiometric coverage, but that dataset was better suited to broad reconnaissance than to detailed target definition.

What the exploration team needed was higher-resolution radiometric data to refine geological models and guide future drilling decisions. Ground surveys could add detail, but in this terrain they were slow, labour-intensive and higher risk.

Altomaxx deployed a drone-based workflow using a Medusa MS-350 gamma-ray spectrometer integrated with the SkyHub onboard computer. Survey lines, flight speeds and elevations were pre-programmed in UgCS and executed through SkyHub.

In this project, the drone flew at approximately 2m/s, producing one raw radiometric point roughly every two metres. Radar altimeters and terrain-aware planning were used to keep the sensor at a more consistent height above uneven, forested ground.

Spatial resolution 

Those details are not just operational colour. In a radiometric survey, height control is part of the measurement method. A lower flight altitude can improve spatial resolution, but inconsistent sensor height can make readings harder to compare across a survey block.

This is why mission planning, altimeter integration and payload synchronisation matter: they connect the geophysical objective to the way the aircraft actually flies.

The same point applies to integration. Radiometric data must be interpreted alongside geology, structure, sampling and other geophysical methods.

SkyHub provided the onboard link between payload acquisition, positioning and flight execution, while UgCS provided the mission-planning environment for repeatable geophysical flight lines. In a remote survey, that repeatability is not a convenience; it is what allows the dataset to be trusted after the crew has left the field.

Radiometric dataset

The result was a UAV radiometric dataset that exceeded the resolution of the earlier helicopter survey. The difference was visible in the data: the helicopter survey established the broader radiometric response, while the drone survey provided a denser view of the anomaly and its internal geometry.

The drone data also revealed additional anomalies that were followed up by geologists on the ground, supporting new mineralisation findings and helping refine drill targeting.

Because the public case study does not disclose gridding or interpolation parameters, the comparison should be read as a reported resolution improvement supported by field follow-up, rather than as a controlled processing comparison. 

For drilling teams, UAV radiometrics does not resolve the geological model on its own. Its value is that it improves the questions asked before drilling begins.

Is the regional anomaly continuous, or does it break into smaller zones? Does the strongest response align with mapped structure or lithology? Is the target broad enough to require more mapping first, or tight enough to justify first-pass drill planning? These are practical decisions, and they are sensitive to data resolution.

The method still has limits. UAV surveys depend on permissions, weather, visual-line-of-sight rules, payload endurance, vegetation height, terrain and follow-up geology.

Crew competence also matters. Flying a UAV radiometric survey to a repeatable standard requires specific skills, including mission planning, payload handling, terrain-aware operation and radiometric survey discipline.

In the Altomaxx project, training was part of the deliverable: the client's team gained the capability to continue drone-based survey work independently in future seasons.

Airborne radiometry

Calibration and field validation should not be treated lightly. Airborne radiometric work relies on standardised measurement geometry and formal correction workflows.

In this project, altitude stability was the core disclosed field-control measure, but all radiometric anomalies still require geological ground follow-up for reliable interpretation.

Drone-based radiometric surveying earns its place in the exploration toolkit through a simple logic: better spatial data supports better-informed targeting, and better targeting can reduce drilling risk.

It is a bridge between helicopter-scale reconnaissance and drilling-scale decisions. Used well, it can turn a broad radiometric response into a more specific target model, reduce uncertainty before field follow-up and give exploration teams a stronger technical basis for deciding where the next drill lines should go. 

*Alexey Dobrovolskiy, is the CEO of SPH Engineering, a company that provides drone-based solutions for site surveying,  inspection and mapping