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Innovative 3D and 2D machine vision methods for analysis of plants and crops in the field

Machine vision systems offer great potential for automating crop control, harvesting, fruit picking, and a range of other agricultural tasks. However, most of the reported research on machine vision in agriculture involves a 2D approach, where the utility of the resulting data is often limited by effects such as parallax, perspective, occlusion and changes in background light – particularly when operating in the field. The 3D approach to plant and crop analysis described in this paper offers potential to obviate many of these difficulties by utilising the richer information that 3D data can generate. The methodologies presented, such as four-light photometric stereo, also provide advanced functionalities, such as an ability to robustly recover 3D surface texture from plants at very high resolution. This offers potential for enabling, for example, reliable detection of the meristem (the part of the plant where growth can take place), to within a few mm, for directed weeding (with all the associated cost and ecological benefits) as well as offering new capabilities for plant phenotyping. The considerable challenges associated with robust and reliable utilisation of machine vision in the field are also considered and practical solutions are described. Two projects are used to illustrate the proposed approaches: a four-light photometric stereo apparatus able to recover plant textures at high-resolution (even in direct sunlight), and a 3D system able to measure potato sizes in-the-field to an accuracy of within 10%, for extended periods and in a range of environmental conditions. The potential benefits of the proposed 3D methods are discussed, both in terms of the advanced capabilities attainable and the widespread potential uptake facilitated by their low cost.

Tokamak-independent software analysis suite for multi-spectral line-polarization MSE diagnostics.

A tokamak-independent analysis suite has been developed to process data from Motional Stark Effect (mse) diagnostics. The software supports multi-spectral line-polarization mse diagnostics which simultaneously measure emission at the mse σ and π lines as well as at two "background" wavelengths that are displaced from the mse spectrum by a few nanometers. This analysis accurately estimates the amplitude of partially polarized background light at the σ and π wavelengths even in situations where the background light changes rapidly in time and space, a distinct improvement over traditional "time-interpolation" background estimation. The signal amplitude at many frequencies is computed using a numerical-beat algorithm which allows the retardance of the mse photo-elastic modulators (pem's) to be monitored during routine operation. It also allows the use of summed intensities at multiple frequencies in the calculation of polarization direction, which increases the effective signal strength and reduces sensitivity to pem retardance drift. The software allows the polarization angles to be corrected for calibration drift using a system that illuminates the mse diagnostic with polarized light at four known polarization angles within ten seconds of a plasma discharge. The software suite is modular, parallelized, and portable to other facilities.

Optimizing a Thomson scattering diagnostic for fast dynamics and high background

The Madison Symmetric Torus (MST) presents challenging conditions for Thomson scattering (TS) measurements. The MST plasmas are reversed-field pinches (RFPs) with electron density n(e)<3x10(13) cm(-3), typically 1x10(13) cm(-3). The TS system was designed to measure from 10 eV to 2 keV; however, six polychromators were upgraded from four to eight spectral channels to resolve to 10 keV. There is no diverter or vertical field, so wall interaction results in high background light both from ion and neutral bremsstrahlungs and from line radiation. Also during standard plasmas, the RFP exhibits regular reconnection sawteeth events during which the plasma current, density, and temperature profiles are flattened. These events are of interest both due to the reconnection physics and to their contribution to the MST equilibrium and confinement. These events occur over 100 microS and exhibit large changes in background light and fast changes in temperature. During improved confinement plasmas, there are no sawteeth; the background is low but the temperature can be over an order of magnitude higher. Data analysis of the system has been developed to accommodate both the large dynamic range of the temperature, the fast dynamics, and the fast changing, high amplitude background. Special attention has been paid to the sources of error, in particular, the contribution of the background. A response-function method reduces the measured uncertainty by a factor of 2. Numerical techniques have been developed which are extremely robust. Two methods are used, a conventional chi(2) minimization using a Levenberg-Marquardt algorithm coupled with Monte Carlo modeling for the error bar and a Bayesian statistics method. The Bayesian method computes the probability distribution for the measured photons and electron temperature and this information can be used to ensemble data and will allow future integrated data analysis efforts.

A new fast-ion Dα diagnostic for DIII-D

The fast-ion Dα (FIDA) technique is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha light from energetic hydrogenic atoms to infer the fast-ion density. Operational experience with the first dedicated FIDA diagnostic on DIII-D is guiding the design of the second-generation instrument. In the first instrument, dynamic changes in background light associated with plasma instabilities usually dominate measurement uncertainties. Accordingly, the design of the new instrument minimizes scattering of cold Dα light while monitoring its level. The first instrument uses a vertical view to avoid bright interference from the injected-neutral beams. The sightline of the new instrument includes a toroidal component but only measures blueshifted fast-ion light that is Doppler shifted away from the redshifted light of the injected neutrals. The new views are more sensitive to fast ions that circulate in the direction of the plasma current and less sensitive to the trapped-ion and countercirculating populations. Details of the design criteria and solutions are presented.

異なる背景光強度におけるイネ生葉のＬＩＦスペクトルと光合成速度の変化

Chlorophyll fluorescence is known to be a sensitive probe of photosynthesis. Laser induced fluorescence (LIF) is useful for remotely sensing physiological information of plants by optical measurement. However, it is difficult to assess the LIF independently because of changes in background light. Background light, like sunlight, not only stimulates photosynthetic reaction but also induces fluorescence.To demonstrate the possibility of detecting changes in photosynthetic reaction according to background light from the LIF spectra, the correlation between LIF spectra and intensity of incident light on leaves was investigated.The LIF spectra from rice (Oryza sativa L.) leaves, which were illuminated with a metal halide lamp as background light, were measured. A gated CCD camera with monochrometer was synchronized to a pulsed UV-laser (Nd: YAG, 355nm) to detect the LIF spectrum under background light of different intensities. The LIF magnitude increased linearly with the laser intensity at each intensity of background light. The slope of fluorescence against laser intensity was considered to be a measure of fluorescent efficiency. The fluorescent efficiency increased with intensity of illumination. This increase of fluorescent efficiency was mainly caused by the increase of blue-green fluorescence (BGF) but chlorophyll fluorescence was constant. These changes of LIF spectra can be explained by the interaction of the fluorescent efficiency of chlorophyll and re-absorption of BGF; these phenomena reflect the redox state of the first electron acceptor (QA) in the photosynthetic reaction. The ratio of regression coefficients of BGF to chlorophyll fluorescence against the laser intensity changed in accordance with the change of photosynthetic rate of rice leaves.Photosynthetic information of leaves was detectable by analyzing the correlation between induction intensity and LIF spectra under changing background light.

Photoreceptor sensitivity changes explain color appearance shifts induced by large uniform backgrounds in dichoptic matching

Photoreceptor sensitivity changes explained the effect of large uniform backgrounds on the color appearance of small targets in a dichoptic asymmetric color matching experiment. Subjects viewed in each eye a target superimposed on a large background. The backgrounds presented to the two eyes had different spectral compositions. Subjects adjusted the target seen by the right eye to match the appearance of the target seen by the left eye. Receptor sensitivity changes explained the effect of numerous adapting backgrounds on the color appearance of many targets with high precision. Post-receptoral sensitivity changes provided a poorer account of the data. The apparent sensitivity of each receptor class varied inversely with changes in background light absorbed by that receptor class, but did not depend on background light absorbed by the other two receptor classes.