Practical Sensor Ranges

As users consider higher flying altitude missions, they'll consider effective and recommended range per-sensor/system. Maximum recommended altitudes vary per sensor, with LiDAR being the most limiting and high-resolution frame cameras typically being the least. We'll breakdown the considerations, limitations, and recommendations for each sensor type, and talk about the specifics of some of our most common sensors.

LiDAR

Largely, the maximum recommended altitude comes down to the practical or effective range of the LiDAR sensor. Sensor specification sheets list a maximum range, and occasionally more in-depth information about range precision at various distances and target reflectivities. As distance to scene increases, both point density and range precision decrease non-linearly. An example using the Ouster OS1-Rev7 is provided below.

According to the sensor specifications, the maximum range is 170 m for targets with 80% Lambertian reflectivity and 90 m for targets with 10% Lambertian reflectivity. This indicates that the sensor's ability to detect dark objects becomes limited beyond approximately 90 m. Vegetation typically has reflectivity values between these two extremes, meaning its effective detection range will generally fall somewhere within this range, depending on the type and characteristics of the vegetation.

GRYFN's test data further illustrates the impact of flying altitude on data quality. For a single flight line, the point density at a flying height of 60 m is approximately 10 times higher than at 120 m. Range precision also degrades as the distance to the scene increases. When a planar surface is extracted from the point cloud and evaluated through plane fitting, the RMS error is approximately 2–3 cm at 60 m, as compared to more than 10 cm at 120 m. In addition, increased flying height is expected to considerably reduce LiDAR penetration and thus fewer ground returns.

At the common maximum legal flying altitude of 120 m over vegetated areas, the OS1-Rev7 can typically still provide usable data for generating digital surface models (DSMs). However, for applications requiring vertical profiles or digital terrain models (DTMs) in canopy-covered areas, we recommend conducting a test flight to evaluate the sensor's performance under the specific operating conditions.

In summary, using the LiDAR data from a higher altitude can be fine, as long as quality loss is understood and accepted, and that raster creation is the primary goal. 

Hyperspectral

Hyperspectral capture is limited primarily by resolution, which extends to visibility of reflectance panels if that will be the utilized method of reflectance conversion. As resolution decreases, fewer reflectance panel target pixels will make up the feature. This can cause challenges when measuring panels in target selection for reflectance ELM calculations. Some options available are using larger panels (GRYFN sells 1m x 1m panel sets intended for high altitudes), or adding additional waypoints and capture polygon areas into the flight plan that image the reflectance panels at a lower altitude. See the Multiple polygons for data capture figure.

Frame Camera

Frame camera data is limited only by resolution. The key consideration, can the sensor still make out the features that are required by the acquisition and research.