Stress caused by increase population density in maize produce significant yield loss. To remedy it, photosynthetic
activity maintenance even under unfavorable conditions is required. Senescence delay induced by stress in stay-green
genotypes (SG) could contribute to maintaining photosynthetic capacity. In this work we observed differences in
reflectance curves of two hybrids (SG and no SG) when population level increased. Significant differences in
chlorophyll absorption spectral region were observed. Therefore spectral signatures studies maize could help to
understanding of the physiological basis of SG character to predict the growing conditions in which these hybrids would
express their production potential.
A low cost portable spectroradiometer able to operate in the 4 bands of the satellite system Landsat MSS was developed. The radiometer was designed to measure the spectral reflectance of spatially extended targets. Spectral bands were selected with 10 nm bandwidth filters. Measurements were made during 2003, from seedtime to harvest, on an experimental plot of wheat. The culture was divided in parcels that received different treatments (seed variety, fertilizer, herbicide and fungicide). Weekly measurements with the detector at nadir and the sun near midday were made. As result of the spectral measurements of reflectance, the normalized difference vegetation index (NDVI) was calculated. As a comparison, LAI, chlorophyll concentration and diverse gravimetric determinations, were carried out. The results were analyzed by means of statistical techniques and showed a good correlation between the optical index and the culture variables. In the future the geometry of the measurement will be improved to reduce the effect of the canopy and other channel in the near infrared will be added to distinguish water and nitrogen stress.
This work continues with the development of a non-dispersive UV optical sensor for stack emissions for SO2 and NO2. These gases are among the most important ones in the emissions of the petrochemical industry. The NDUV consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter centered at each channel's wavelength, and a photodiode with control electronics. Calibration curves and the effect of cross interference on concentration measurements of these gases are shown.
A school optical equipment has been designed and developed. It is the result from the cooperative activities of researchers and experts in didactic of the science. The equipment includes a handbook, experimental guides and proposals to be carried in the classroom.
12 Optical spectroscopy related to analytical techniques have attracted much interest in recent years and became a central part of versatile instruments used for trace gas monitoring. Optical methods are based on different interactions between radiation and matter (absorption, emission and scattering) and use different sources of radiation such as conventional lamps, lasers, the sun, etc. Differential Optical Absorption Spectroscopy is a good example of these kind of techniques where commercial instruments are available today. Typically, it consists of a collimated broadband radiation source that shines a beam of light through an open atmospheric path several hundred meters long; at the other end, a receiving telescope is located which focus the beam on a medium resolution spectrometer-photodetector system that analyzes the wavelength spectrum of the incoming light within a certain range. The absorption bands of a specific gas component failing in this range are thus detected. For multicomponent analysis, the spectrometer must be scanned across different wavelength ranges introducing potential error sources.
12 Non-dispersive analyzers have been used for measurement of gases for many years and were recently introduced as on-line meters for continuous stack emission measurements in industrial plants. SO2 and NO2 are among the most important gases in the emissions of the petrochemical industry. The development of a UV-visible meter for these gases is presented. It consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter of 10 nm bandwidth centered at each channel's wavelength. Each filter is followed by a photodiode and its electronics which are housed in a single compartment with no moving parts. An incandescent lamp with high output in the UV region was selected and mounted on the opposite side of the stack by appropriate flanges. The equipment was designed to measure in the range between 0 and 500 ppmv with a resolution of about 2 ppmv. Performance parameters like signal stability, dark current, detection limit and calibration curves are shown.
A sun-photometer designed for aerosol studies was built and it was installed permanently at San Luis City, Argentina. This instrument measures the attenuation of direct solar light at wavelengths were molecular absorption are minimal, 380 nm, 500 nm, 770 nm, and 1060 nm. It makes continuous measurements mounted on a solar tracker and data are filed every minute. An extra channel at 940 nm was introduced for water measurements. Results in San Luis confirm that aerosols normally present in that place are dust-like particles with a very shallow extinction spectrum. Such aerosols can not be represented by the standard form of the angstrom's formula where (alpha) equals 1.2 is normally assumed. This fact must be taken into account when radiative-transfer models are used, specially in the UV region. During two short periods of time, the meter was operated at different places: Las Cuevas, at 3200 m height at Los Andes mountains, and Pampa Amarilla, the site for a future cosmic ray observatory in Argentina. Typical results for these geographical regions corresponded to clean atmospheres with small quantity of large particles. The water channel was calibrated by simultaneous measurements with a Microtops II, a commercial sun-photometer; in the near future the radiometer will be contrasted against water-radiosonde measurements.
A three-wavelength sun-photometer was designed and built. The attenuation of direct solar light, at wavelengths of 0.38 micrometers , 0.50 micrometers and 1.00 micrometers were measured. Silicon photodiodes and interference filters of 10 nm FWHM were used. Aerosols were characterized by angstrom's turbidity formula in terms of coefficients (alpha) and (Beta) and by Moon's model in terms of the precipitable water content, w, and the amount of dust particles per unit volume, d. Aerosol attenuation was calculated from the slope of Langley's plots. Several measurements were performed in the city of San Luis during summer and autumn seasons of 1996. Results corresponded to a very clean atmosphere. Weather was extremely dry during most of measurements.
Three optical methods for sizing polymer particles are instrumented to be used in the leather industry. One method is based on the measurement of the light scattered intensity for several angles, and the other two are monochromatic or spectral extinction methods. Uniform latex particles and two commercial products used in leather finishing are measured. Advantages compared with electronic microscopy are discussed.
Measurement of optical absorbance is used to study the relaxation of acrylic film doped with Disperse Red 1 and poled with an electric field produced by the corona effect. Time variation of dichroism is studied over 10 days and results are adjusted with different time functions. Second-harmonic generation is presented as a test of the lack of symmetry of the poled film resulting from the orientation process.
Continental Argentina and Chile are extended on a very dangerous geographic situation in relation with the ozone layer depletion. Global reduction in total ozone can be related in part with the Antarctic's ozone hole and its dynamics of dilution; this phenomena is not well studied yet. To follow this process, a network of 16 simple and portable ozone meters has been developed. The instruments, installed from Arica (18 S) to Rio Grande (54 S), work by measuring the direct solar intensity at 300 nm and 313 nm. The ratio of these two measurements was related directly with ozone contents. Measurements during 1993 and 1994 have shown that when the ozone hole reached South America, a correlated reduction in the total ozone content can be observed in latitudes as low as 35 S. The origin of the ozone depletion detected over Argentina and Chile is discussed in relation with solar flares and circulatory dynamics.