Harnessing the efficiency of airborne geophysical technology to accurately model height reference surfaces based on the Earth’s gravity field

A geoid is a model of the Earth’s surface that reflects mean sea level on shore and corresponds to a flat and level surface within the Earth’s gravity field.

This “flat” level surface is used alongside GNSS (Global Navigation Satellite Systems) coordinated height data to determine precise physical heights, providing essential context for elevation data across various applications. The geoid can be thought of as the physical reference surface from which physically meaningful elevations can be measured.

Geoid models are critical a critical component of positioning infrastructure, with applications which include:

• Surveying and Mapping: They enable efficent GNSS height measurements, for engineering and construction projects.
• Flood Risk Assessments: They underpin analysis determining water flow patterns and coastal inundation modelling.
• National Height Datum: They facilitate a unifies reference surface for measuring hights across a country, critical for infrastructure development and geographic data consistency.
• Critical National Positioning Infrastructure: The support geodetic and GNSS networks, vital for navigation, transportation, and land management.

We offer airborne gravity surveys specifically tailored for geoid modelling and data processing services to deliver geoid models that meet the highest standards. Using our proprietary iCorus-iX scalar gravimeter, we capture gravity data suitable for cm level accurate geoid modelling from the air, allowing for seamless and efficient data capture over large and otherwise inaccessible areas.

• Scalar Absolute Gravimetry: We use the iCorus-iX gravimeter to measure gravity anomalies at a 3 km spatial resolution. The system provides high accuracy, with gravity anomalies accurate to within 1-2 mGal.
• Survey Design: Flights are conducted at tailored altitudes and line spacings to ensure full coverage of the area. Depending on terrain and specific project needs, we adjust flight parameters for optimal downstream geoid modelling.

Data Processing and Modelling

After data capture, we process the collected data through several key steps:

• Gravity Anomalies: We reduce the gravity data to anomalies on a line-by-line basis, applying time domain filters to remove any artifacts associated with system dynamics during data capture.
• Least Squares Collocation: This method is used to interpolate gravity anomaly data in three dimensions onto regular grids at the topographic surface, as well as directly model the disturbing potential from scalar gravity anomalies.
• Transformation of Potential into a Reference Surface: The final transformation from potential into the reference surface is tailored to meet the client’s specific needs—whether producing a quasi-geoid by applying Bruns’ equation directly or applying additional topographic compensations (e.g., the Poincaré-Prey approach) to generate a true geoid.
• Uncertainty Quantification: Uncertainty is propagated through the least squares collocation method and final transformations, providing estimates of accuracy for both the gravity anomalies and the resulting geoid model.

• Gravity Anomalies and Interpolation: Gravity anomalies are processed at flight altitudes, then interpolated into regular grids as per client specifications. The anomalies are processed specifically for geoid modelling, e.g. using orthometric heights during the reductions. The interpolation includes a downward continuation of the gravity data to the surface of the topography.
• Data fusion: Additional data sources can be ingested during the interpolation phase using Least Squares Collocation to augment the airborne data with any existing high-fidelity gravity data coverage, or GNSS-levelled heights.
• Remove-Compute-Restore Scheme: To ensure high precision in the long wavelengths, we use global spherical harmonic models (e.g., EGM2008) to adjust for large-scale gravity variations, allowing us to focus on the finer details of the local gravity field.

Why Choose Us?

Our expertise in airborne geophysics and geoid modelling ensures that you receive the most accurate, reliable, and timely data for your project. Whether it’s national-scale surveys or specialized local models, our team is equipped to meet the most rigorous requirements.