The number of returns, also referred to as echoes, is the sensor’s ability to capture multiple returns from a single emitted pulse. More returns are beneficial for canopy mapping missions where the top of the canopy and the ground below the canopy need to be reconstructed. LIDAR systems equipped on sUAS typically have two-five returns.

The scan rate is the number of laser pulses the sensor emits per second. This specification, along with the distance away from the area of interest, affects the number of points per square meter in the resulting data.  

The trigger speed or frame rate of an imaging sensor impacts the maximum speed of the aircraft to still collect good information. This limitation is determined by the write speed of the sensor. For example, triggering too fast could lead to skips. Also note, flying too fast will lead to undesirable image artifacts such as motion blur and an inability to achieve the desired overlap.

The focal length is the distance of the focal point of the lens to the imaging sensor. For the same imaging sensor, a larger focal length means a smaller field of view and more detail than a lower focal length which has a wide field of view with less detail. For structure from motion mapping, focal length is typically in a range of 5-30mm. In summary, the focal length affects the field of view of the sensor and the image’s spatial resolution. This will affect the required flight altitude and side-lap to achieve respective spatial resolution and side-lap percentage.

The pixel rows and columns, or pixel dimensions, is the number of pixels within an imaging sensor. This directly affects the spatial resolution; more pixels mean higher spatial resolution. The number of pixels also has ties to the next tab, sensor length & width.

The sensor length and width are the physical dimensions of the imaging sensor chip. This is usually measured in millimeters. The number of pixels and the dimensions of the sensor determines the size of the pixels. Larger pixels are better because they can collect more light information, thus improving the signal to noise ratio of the image. This is especially helpful for light-starved scenes.