Currently sophisticated methods of airborne laser scanning are in development. Analysing in more detail the reflection signals (full waveform) can improve the information that is gathered about the target objects [19-21].Low cost sensors do not have this option. Under such conditions the problem of how to assess the readings seattle genetics of simple sensors with only one echo when the beam targets different crops or soil surfaces remains unanswered.As far as the beam guidance aspect is concerned, we can distinguish between sensors with a fixed beam and those with a scanning beam. For laser scanners there are limited opportunities for the users to influence the movement of the beam. For lasers with a fixed beam individual solutions can be developed by moving the entire sensor housing with some corresponding kinematics.
In the field of agricultural engineering research, low cost laser rangefinders available in the marketplace have been investigated in both horticulture and in agriculture seattle genetics applications. In horticulture Tumbo et al. measured the canopy volume and structure in citrus . Walklate et al. compared different spray volume deposition models using LIDAR measurements of apple orchards . Sanz et al. reported on advances in the measurement of structural characteristics of plants (peach trees) with a LIDAR scanner . Escola et al. investigated a variable dose rate sprayer prototype for tree crops based on sensor measured characteristics .In agriculture Th?sink et al. made a first test to measure the height of oat plants .
To calculate the crop height, the level of soil surface was discriminated from the distribution of height classes. seattle genetics Kirk et al. estimated in a comparative study the canopy structure from laser range measurements and computer vision . Ehlert et al. measured crop biomass density in oilseed rape, winter rye, winter wheat and grassland by laser triangulation . Lenaerts et al. predicted crop plant density using LIDAR-sensors .Ehlert et al. assessed low cost laser rangefinders for vehicle-based measurement of crop biomass . High functional correlations were found between mean reflection height hRmean (m) �C calculated from measured reflection range and sensor height �C and fresh crop biomass density FMD (kgm-2). In oilseed rape, winter rye and winter wheat crops, the goodness of fit for a linear regression was more than 0.
90 (R2 > 0.9). In grassland (pasture) the accuracy was lower. This can be explained by the occurrence of several plant species with variable morphology and the small dimensions of leaves and stems (Table 1).Table 1.Coefficients of determination for the relationship between crop biomass density and mean reflection height for small ranges < 2.50 m In these measurements the beam was either directed down at the crop plants or was pivoted around a horizontal axis of ��15�� (Figure 1). Due to the mounting height of the sensor the measuring range was less than 2.5 m.