Methodology

Our Methodology

Southern Mapping Company’s airborne laser survey equipment consists of a specialised laser terrain mapper (Lidar), a high-resolution digital photo camera, a video camera, and various controllers.
We consider high mobility of the laser survey equipment of utmost importance. This gives us the opportunity of operating our system worldwide.

The way Lidar operates has much in common with a typical radar system. Lidar pulses a laser beam onto the periodically oscillating mirror and projects it downward. The laser beam hits an object and reflects back to the mirror.

The scanner receives reflections of all the objects within the area needing to be surveyed. High-speed counters measure the time interval between the pulse leaving the airborne platform and its return to the Lidar sensor. Lidar time-interval measurements are converted to distances and correlated to the information recorded by GPS receiver, Inertial Measurement Unit (IMU), and ground-based GPS stations.

3-dimensional GPS solution is used to position the laser scanner at each second or half second, while the IMU data is used to determine the system’s orientation.

Our system is capable of discriminating among multiple returns from each pulse measuring not only the position and geometry of the surface below the aircraft, but also the terrain under the vegetation cover.

Our methodology consists of three phases:
- Registering Phase
- Intermediate Phase
- Final Phase

By using these phases, Southern Mapping have a distinct advantage of being able to identify and measure the position of on-ground objects, map the land surface under the vegetation layer and obtain spatial model of vegetation.

This important feature of the system is used with data processing algorithms to create a digital terrain model not affected by the vegetation.

We perform a calibration flight to ensure the system meets specifications. Preliminary data processing is conducted to ensure completeness and integrity. This acts as a quality control process thus ensuring that coverage is complete and that the equipment was functioning well. Should there be a gap or unacceptable data quality detected, the crew will isolate problem areas and re-fly the affected sections before demobilising. The GPS and inertial data are processed together to achieve the best positional result. Once the position and attitude of the aircraft are known at each period (1 or 0.5 -second intervals), this data is integrated with the laser reflections to provide a position for each point on the ground. The data is processed using the proprietary laser-processing software suite to produce an ASCII file of (x,y,z) coordinates.

Towards the final product output various operations are performed over the collected survey data. These include the initial laser points computation, laser data classification points, objects recognition, digital photographs, thematic objects processing and others in accordance with the client’s requirements. All operations are performed in conjunction with a stringent quality assurance plan, which forms part of the contract. It’s the final product of our services that sets us apart from other lidar companies. We dedicate our efforts, in first ensuring that we fully understand our clients’ needs and expectations. In so doing we deliver quality solutions that assist you in maintaining efficiency of your business.

Lidar Technology

Lidar (Light detection and ranging) technology uses laser distance measuring technology to conduct topographic mapping. Unlike other technologies, lidar beams, which are transmitted from the aircraft, are able to function in overcast and cloudy conditions and can penetrate through dense vegetation. Lidar provides high accuracy at much higher speeds.

This lidar system measures distances directly from the aircraft to the ground during flight, using laser ranging. When combined with a digital camera, high resolution, full colour imagery is created.

During aerial surveys the laser fires 100,000 laser pulses per second at 25 degrees left and right of the direction of the flight of the aircraft. Simultaneously the camera takes photos of the earth below which are then draped in their precise location on the 3D model. The aircraft’s trajectory and movements are kept carefully in check by means of a GPS and an Inertial Navigation System (INS).

Advantages of lidar technology

- Vegetation Penetration: Lidar has a very narrow beam which is emitted from the aircraft. This beam can penetrate dense foliage to reflect off the ground and return to the aircraft.
- Accuracy: A terrain model of extremely high accuracy can be delivered, due to the sheer density of the laser points.
- Ground control: No ground control is required because of the accurate measuring equipment in the aircraft i.e. the GPS and IMU. Hence the entire project can be calculated from airborne sensors. The ground survey equipment of a lidar project is far simpler than a conventional survey. Hence it is faster.
- Weather conditions: Lidar is an active sensor and therefore does not require ambient light to function. Many projects have been successfully completed in overcast or partly cloudy conditions.
- Digital workflow: The lidar and camera both deliver their raw observations to computer disc in the aircraft. Once the sortie is completed, the air operator delivers the removable disc drives to the processor. The processor then immediately works on data processing. Within hours, verification of the day’s mission is completed. The entire project is usually processed, verified and delivered to our clients within 30 days. This is by far, faster than any other technology.