Characterizing and Estimating Fungal Disease Severity of Rice Brown Spot with Hyperspectral Reflectance Data

Large-scale farming of agriculture crops requires real-time detection of disease for field pest management. Hyperspectral remote sensing data generally have high spectral resolution, which could be very useful for detecting disease stress in green vegetation at the leaf and canopy levels. In this study, hyperspectral reflectances of rice in the laboratory and field were measured to characterize the spectral regions and wavebands, which were the most sensitive to rice brown spot infected by Bipolaris oryzae （Helminthosporium oryzae Breda. de Hann）. Leaf reflectance increased at the ranges of 450 to 500 nm and 630 to 680 nm with the increasing percentage of infected leaf surface, and decreased at the ranges of 520 to 580 nm, 760 to 790 nm, 1550 to 1750 nm, and 2080 to 2350 nm with the increasing percentage of infected leaf surface respectively. The sensitivity analysis and derivative technique were used to select the sensitive wavebands for the detection of rice brown spot infected by B. oryzae. Ratios of rice leaf reflectance were evaluated as indicators of brown spot. R669/R746 （the reflectance at 669 nm divided by the reflectance at 746 nm, the following ratios may be deduced by analogy）, R702/R718, R692/R530, R692/R732, R535/R746, R521/R718, and R569/R718 increased significantly as the incidence of rice brown spot increased regardless of whether it＇s at the leaf or canopy level. R702/R718, R692/R530, R692/R732 were the best three ratios for estimating the disease severity of rice brown spot at the leaf and canopy levels. This result not only confirms the capability of hyperspectral remote sensing data in characterizing crop disease for precision pest management in the real world, but also testifies that the ratios of crop reflectance is a useful method to estimate crop disease severity.

Comparative Study on the Infrared Radiance Field of Building Surface under Sunshine Conditions and Rainfall Conditions

The Monte Carlo method and the region method are combined in this paper,where a high-rise building in Harbin were taken for example to investigate the infrared radiation field of building surface.The calculation models of temperature field and radiation transfer coefficient on the exterior surface were established.Through the self-built Bidirectional Reflectance Distribution Function(BRDF)experimental device,the BRDFs of moorstone,aluminum plate,coated glass and Ethylene-Propylene-Diene Monomer(EPDM)on the surfaces under dry and wet conditions were measured at different incidence angles with respective laser wavelengths of0.6328μm and 1.34μm.For the two wavelengths,the reflection ratios of the material surfaces under dry and wet conditions were calculated respectively.Based on some proper simplifications of the background condition,the simulation analysis of the radiation field of building surface was carried out according to the wetness theory and the measured data.Taking the situation at 9:00 a.m.on the day of summer solstice as an example,this paper made relevant quantitative calculation for the solar radiation,the self radiation of the surface units,the radiating projection between the surface units,and the general infrared radiation of the building surface.Comparisons on infrared radiance field of the building surface were obtained under cloud-free sunshine conditions and rainfall conditions respectively,and the rationality of the results was discussed.