Abstract
Abstract A method is developed for processing pictures taken from multicopters in order to identify the number of Caspian seals and their linear sizes on rookeries. A special protocol records the location (coordinates), date, time, survey altitude, the cloudiness across a scale ranging from one to ten, air temperature, wind speed, and picture numbering. A photo software editor (for example, Adobe Photoshop CS5) is used for counting the individuals and taking their measurements. Each seal image is allotted an individual serial number within one picture. By flying over and photographing a rookery at different times of the day, quadcopters allow for an assessment of the daily dynamics of the seal numbers to be made. In cases when the groups under assessment are numerous, counts are recommended to be performed along transects. Knowing the angle of the field of vision (FOV) of the multicopter and the altitude it operates at, the following formula can be applied, “A cathetus lying opposite the angle equals the product of the second cathetus multiplied by the tangent angle,” to calculate the distance between the extreme points of a picture’s diagonal in the International System of Units (m, cm, or mm) (SI). As the resolution in pixels is also known, calculating the size of a pixel in SI can be performed per picture. The measurements of individual seal images in the pictures are converted from pixels into SI units. As a result, the length and the maximum width of the seals can be established, this being of importance for identifying the size structure of the seal concentrations on rookeries. Subsequently, having compiled a size–age key, the age structure of the groups of seals on rookeries can be calculated.