F. Carvajal

Geometric accuracy assessment of the orthorectification process from very high resolution satellite imagery for Common Agricultural Policy purposes

This study has, as its main aim, the assessment of different sensor models to achieve the best geometric accuracy in orthorectified imagery products obtained from IKONOS Geo Ortho Kit and QuickBird basic imagery. The final orthoimages are compared, both geometrically and visually, with the panchromatic orthophotos based on a photogrammetric flight with an approximate scale of 1 : 20 000, which are now used for the European Union Common Agricultural Policy in Andalusia (Spain). Two‐dimensional root mean square (RMS2d) errors in independent check points are used as accuracy indicators. The ancillary data were generated by high accuracy methods: (1) check and ground control points (GCPs) were measured with a differential global positioning system and (2) an accurate digital elevation model was used for image orthorectification. Two sensor models were used to correct the satellite data: (1) a three‐dimensional (3D) rational function refined by the user with zero‐ (RPC0) or first‐(RPC1) order polynomial adjustment and (2) the 3D Toutin physical model (CCRS). For the IKONOS image, the best results in the final orthoimages (RMS2d of about 1.15 m) were obtained when the RPC0 model was used. Neither a large number of GCPs (more than nine), nor a better distribution of them, improved the results obtained with the RPC0. For the QuickBird image, the CCRS model generated the best results (RMS2d of about 1.04 m), although it was sensitive to the number and distribution of the GCPs used in its computation.

Field evaluation of a self-propelled sprayer and effects of the application rate on spray deposition and losses to the ground in greenhouse tomato crops

BACKGROUND In the greenhouses of south-eastern Spain, plant protection products are applied using mainly sprayers at high pressures and high volumes. This results in major losses on the ground and less than uniform spray deposition on the canopy. Recently, self-propelled vehicles equipped with vertical spray booms have appeared on the market. In this study, deposition on the canopy and the losses to the ground at different spray volumes have been compared, using a self-propelled vehicle with vertical spray booms versus a gun sprayer. Three different spray volumes have been tested with a boom sprayer, and two with a spray gun. RESULTS The vehicle with the vertical spray boom gave similar depositions to those made with the gun, but at lower application volumes. Also, the distribution of the vertical spray boom was more uniform, with lower losses to the ground. CONCLUSIONS The vertical spray booms used in tomato crops improve the application of plant protection products with respect to the spray gun, reducing the application volumes and the environmental risks of soil pollution.

Relationship between atmospheric corrections and training-site strategy with respect to accuracy of greenhouse detection process from very high resolution imagery

Frequently, satellite images that are acquired to extract a target surface are atmospherically corrected prior to the detection process. Thus, the unification of measure units is achieved, and atmospheric effects are removed from various imagery sources or taken at different dates. In this paper, four increasing levels of atmospheric corrections are applied (Top-Of-Atmosphere transformation: TOA; Apparent Reflectance Model: ARM; Flat Areas Model: FAM; Non-Flat Areas Model: NFAM). Then, the classification process is carried out using two strategies of training-site definitions (statistically purified and crude training sites) and two satellite imagery sources (QuickBird and Ikonos). Three-way Analysis of Variance (ANOVA) tests and Fishers least-significant difference tests are included in quality classification assessment, based on four accuracy indexes. Two images from both remote sensors are orthorectified, and then it is checked that all selected atmospheric correction levels have significantly different influences on the statistics of both orthoimages. Taking into account the conditions established in this work, it is concluded that a lower atmospheric correction level would be preferred because it does not present significantly worse results than other levels considered. Training sites would not be statistically purified, and QuickBird or Ikonos would be chosen, depending on the aspect of the greenhouse detection accuracy preferred.

Atomization characteristics of hydraulic nozzles using fractal geometry

Fractal scalings of the V(x X) . Xd type have been used in this work for cumulative volume (V) distribution applied through spray nozzles in size x droplets, smaller than the characteristic size X. From exponent d, the fractal dimension (Df), which measures the degree of irregularity of the medium, has been deduced. This property consists of the repetition of the irregularity itself over a certain range of scales, and it is called self-similarity. The objects or sets that have this property are named fractals. Based on the considerations below, and supposing that the droplet set from a spray nozzle is self-similar, an algorithm has been developed to relate a nozzle type with a Df value. The data input for this algorithm were the droplet size spectra factors corresponding to 10%, 50%, and 90% (Dv0.1, Dv0.5, and Dv0.9, respectively) as measured at different operating pressures for different nozzle types. Multivariate, multilinear, and polynomial models were conducted to predict droplet size spectra factors based on Df and operating pressure (multilinear model) and based on Df, operating pressure, and orifice diameter (polynomial model). Df values showed dependence on nozzle geometry and independence of operating pressure. Significant coefficients of determination (r2) at the 95% confidence level were found for the fitted models. An exception occurred in one case, associated with Dv0.9. Thus, r2 values were higher for the polynomial models than for the multilinear models, except for a case associated with Dv0.1. These models could be useful to compare the behavior of different nozzles under the same operating conditions, or the same nozzle under different operating conditions. Because Df is related to nozzle geometry, the inclusion of Df in models to predict droplet size spectra factors will allow us to detect the geometric differences between nozzles, which are otherwise difficult to measure. Similar procedure could be carried out for other nozzles types.