Real-time Soil Sensing with NIR Spectroscopy
The grey-brown alluvial soil is a typical soil in the Northern China. It was selected as research object to reveal feasibility and possibility of real-time analyzing soil parameter with NIR spectroscopic techniques. 150 samples were collected from a winter wheat farm. And then the NIR absorbance spectra were rapidly measured under the original conditions by a Nicolet Antaris FT-NIR analyzer. Three soil parameters, soil moisture, SOM, TN content, were analyzed. For soil moisture content, a linear regression model was available, using 1920 nm of wavelength with correlation coefficient of 0.937, So that the results obtained could be directly used to real time evaluate soil moisture. SOM content and TN content were estimated with a multiple linear regression model, 1870nm and 1378nm wavelengths were selected in the SOM estimated model, while 2262nm and 1888nm wavelengths were selected in the TN estimated model. The results showed that soil SOM and TN content could be evaluated by using NIR absorbance spectra of soil samples.
Discrimination of Australian soil horizons and classes from their visible–near infrared spectra
A soil's reflectance spectrum in the visible and near infrared is rich in information. It is an integrative property of the soil that measures its colour, the abundance of iron oxides, clay minerals and carbonates, the amount of water and organic matter and its particle size. We explored the merit of discriminating between soil horizons, of which we had 13 654 samples, and soil orders from the Australian Soil Classification, of which we had samples from 1697 profiles with designated horizons, by analysing quantitatively their diffuse reflectance spectra in the visible‐near infrared (vis–NIR) range (350–2500 nm).
Theoretical analysis of a new family of geodesic lenses
The design of a new family of geodesic lenses is described as a particular solution of the previously known analytic general procedure [ S. Sottini V. Russo G. C. Righini , J. Opt. Soc. Am.69, 1248 ( 1979)]. The lens profile is simplified to make the fabrication easier. Moreover, the profile curvature is always sufficient to prevent guided-light leakage. Two approximations have been introduced into the design procedure. Their effects on the lens performance have been evaluated by ray tracing, and a few simple criteria have been found that permit lenses of any focal length to be designed with a diffraction-limited aperture as large as 62% of the depression diameter.