J. Lichtenberger

Crop yield estimation by satellite remote sensing

Two methods for estimating the yield of different crops in Hungary from satellite remote sensing data are presented. The steps of preprocessing the remote sensing data (for geometric, radiometric, atmospheric and cloud scattering correction) are described. In the first method developed for field level estimation, reference crop fields were selected by using Landsat Thematic Mapper (TM) data for classification. A new vegetation index (General Yield Unified Reference Index (GYURI)) was deduced using a fitted double-Gaussian curve to the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) data during the vegetation period. The correlation between GYURI and the field level yield data for corn for three years was R 2=0.75. The county-average yield data showed higher correlation (R 2=0.93). A significant distortion from the model gave information of the possible stress of the field. The second method presented uses only NOAA AVHRR and officially reported county-level yield data. The county-level yield data and the deduced vegetation index, GYURRI, were investigated for eight different crops for eight years. The obtained correlation was high (R 2=84.6–87.2). The developed robust method proved to be stable and accurate for operational use for county-, region- and country-level yield estimation. The method is simple and inexpensive for application in developing countries, too.

Yield estimation for corn and wheat in the Hungarian great plain using Landsat MSS data

Abstract Models for the forecasting of crop yields using remotely-sensed satellite data are studied intensively worldwide. After reviewing the experience gained by other researchers in this field, we selected procedures which might be suitable for the estimation of corn and wheat yields in Hungary. In order to study the relations between various remotely-sensed spectral data (and their combinations) and the actually measured final yields we investigated archived agricultural and Landsat MSS spectral data for 1984. A linear relation has been sought and found between the yield data for 47 corn and 55 wheat fields in Hajdu-Bihar county and various weighted and summed spectral quantities. Among the vegetation indices derived from satellite data and corrected for atmospheric effects the most promising were the spectral indices sensitive to the green biomass. The latter, summed over a certain period in the growing season, exhibited a regression of 45-86 per cent, depending on the crop and the period of summatio...

Fine structure of whistlers recorded digitally at Halley, Antarctica

Abstract Two whistlers recorded digitally at Halley, Antarctica (L = 4.3) were analyzed by matched filtering with 10 Hz frequency resolution. For the construction of the matched filter, a more realistic description of the whistler waveform than has been used for lower latitude whistlers was applied. The ( ƒ, t ) pairs obtained, together with the corresponding magnitudes, gave a high resolution dynamic spectrum which revealed the fine structure of the whistlers. Whistlers which appeared as well defined, discrete, single traces on a conventional spectrogram, turned out to be composed of several components covering various parts of the spectrum. Further analysis of the strongest and longest component of a whistler resulted in high resolution travel time residual curves similar to those obtained by the ray tracing method or by averaging of numerous occurrences of whistlers in the same duct. The matched filter method of analysis can provide new insights into the details of ducted whistler propagation. It also yields the amplitude variation vs time (or vs frequency) along the whistler trace, thus potentially giving information about the spectrum of the source spheric, and/or the frequency dependence of magnetospheric amplification due to wave-particle interactions.

Trace splitting of whistlers: A signature of fine structure or mode splitting in magnetospheric ducts?

Previously, we reported on the discovery of fine structure in whistler data received on the ground at Halley, Antarctica. This structure was not apparent in conventional spectral analysis but was revealed by the technique of digital matched filtering. We have now examined a larger data set, and a commonly observed phenomenon is that single whistler traces become split into two, over various frequency ranges. Examples are presented in the form of time-transformed spectrograms in which reference model whistlers are represented as vertical lines. The splitting is typically 5–15 ms (about 0.5% of the total whistler travel time) and extends over frequency ranges of a few hundred hertz which may occur anywhere between the upper and lower cutoff frequencies of the whistler. The splitting may be either symmetrical or unsymmetrical with respect to the unsplit trace. The effect is unlikely to arise in the spectrum of the lightning source or from propagation under or through the ionosphere. It may, however, be a signature of field-aligned fine spatial structure in plasmaspheric density, and hence refractive index, in the whistler duct. For simple longitudinal propagation, electron density fluctuations of the order of 1% and spatial scale sizes of the order of 50 km in the equatorial plane are implied. It seems possible that the observations could also be interpreted in terms of the mode theory of ducted propagation, assuming the excitation of two modes with group velocities differing by a few tenths of a percent.

Correction of atmospheric effects of satellite remote sensing data (Landsat MSS-NOAA AVHRR) for surface canopy investigations

Abstract A new correction method for atmospheric effects in Landsat-MSS and NOAA AVHRR data is presented which uses only the remotely-sensed multispectral data. The method is based on a new quasi-single-variable radiative transfer model, and as a first step we assumed that the surface is covered by vegetation. For Landsat-MSS data the method was developed for the tasseled cap indices using known empirical relationships among them. For NOAA AVHRR data ‘ cap-like’ indices and the average reflectance of the average canopy in the visible band known from Landsat-MSS data were used. The method was used in yield forecasting project in north-eastern part of Hungary and provided a significant enhancement in the quality of remotely sensed data.

Two and three component direction-finding computations on whistlers using the Matched Filtering and Parameter Estimation method

A detailed frequency analysis of the azimuthal bearing of ground-observed whistlers by the modified MFPE method (Lichtenberger et al., 1987) based on two and three component digital recordings is presented. Theoretical model calculations by Strangeways (1980) and Strangeways and Rycroft (1980) on systematic azimuthal bearing errors of direction-finding systems are confirmed. Further, directionfinding systems (based on three measured components that do not suffer from polarization error) have no advantage in practice, and are inferior to simple crossed-loop goniometer systems. The MFPE method simulating the latter can be used as a tool for investigating whistler ducts and hence plasmaspheric drifts. An example of this is presented.

Surface models including direct cross-radiation: a simple model of furrowed surfaces.

Abstract In the interpretation of measured reflectance data it is important to consider those surface radiation effects which make a significant contribution to the overall irradiation pattern. A model was constructed for furrowed bare soil surfaces which includes the direct cross-radiation effect between the surface elements. According to the model computations performed the direct cross-radiation plays a significant role in the measured, reflected signal intensity. The computational method developed is suitable for including the direct cross-radiation effect in surface radiation models in the optical region.

Probability density functions for the variable solar wind near the solar cycle minimum

Unconditional and conditional statistics are used for studying the histograms of magnetic field multiscale fluctuations in the solar wind near the solar cycle minimum in 2008. The unconditional statistics involves the magnetic data during the whole year in 2008. The conditional statistics involves the magnetic field time series split into concatenated subsets of data according to a threshold in dynamic pressure. The threshold separates fast-stream leading edge compressional and trailing edge uncompressional fluctuations. The histograms obtained from these data sets are associated with both multiscale (B) and small-scale (δB) magnetic fluctuations, the latter corresponding to time-delayed differences. It is shown here that, by keeping flexibility but avoiding the unnecessary redundancy in modeling, the histograms can be effectively described by a limited set of theoretical probability distribution functions (PDFs), such as the normal, lognormal, kappa, and log-kappa functions. In a statistical sense the model PDFs correspond to additive and multiplicative processes exhibiting correlations. It is demonstrated here that the skewed small-scale histograms inherent in turbulent cascades are better described by the skewed log-kappa than by the symmetric kappa model. Nevertheless, the observed skewness is rather small, resulting in potential difficulties of estimation of the third-order moments. This paper also investigates the dependence of the statistical convergence of PDF model parameters, goodness of fit, and skewness on the data sample size. It is shown that the minimum lengths of data intervals required for the robust estimation of parameters is scale, process, and model dependent. ©2015. American Geophysical Union. All Rights Reserved.

Yield forecasting for wheat and corn in Hungary by satellite remote sensing

We have developed an advanced version of our yield estimation method [Ferencz et al., 2004, Crop yield estimation by satellite remote sensing. International Journal of Remote Sensing, 25, pp. 4113–4149], that is able to provide reliable forecasts for corn and wheat, several weeks before the harvest. The forecasting method is based on the data of the Advanced Very High Resolution Radiometer (AVHRR) instruments of the National Oceanic and Atmospheric Administrations (NOAA) Polar Orbiting Environmental Satellites (POES). The method was applied to Hungary between the years 1996 and 2000. The forecasted yield values are all within 5% reliability with respect to the actual yield data produced by classic (non-satellite based) methods and provided by the Hungarian Statistical Office, with the exception of 1997, where the absolute error is about 8%.

Very low latitude (L = 1.08) whistlers and correlation with lightning activity

We present analysis of more than 2000 lightning-generated whistlers recorded at a low-latitude station, located at Allahabad (geographic latitude, 25.40°N; geographic longitude, 81.93°E; L = 1.081), India, during December 2010 to November 2011. The main focus of this work is on the correlation between observed low-latitude whistlers and lightning activity detected by the World-Wide Lightning Location Network near the conjugate point (geography 9.87°S, 83.59°E) of Allahabad. Whistler occurrence is higher in the postmidnight period as compared to the premidnight period. Whistlers were observed in the daytime only on 2 days that too before 8:30 LT (morning). Seasonally, occurrence is maximum during winter months, which is due to more lightning activity in the conjugate region and favorable ionospheric conditions. About 63% of whistlers were correlated with lightning strokes in the vicinity of the conjugate point within spatial extent of 1000 km (conjugate area). Most (about 53%) whistlers were found to be associated with lightning strokes that were offset to the southeast of the conjugate point. The results indicate that an energy range of 7.5–17.5 kJ of lightning strokes generate most of whistlers at this station. The L shell calculations show that propagation paths of the observed whistlers were embedded in the topside ionosphere. Based on these results we suggest a possibility of ducted mode of propagation even for such very low latitude whistlers.