Cs. Ferencz

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.

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.

Real solution of monochromatic wave propagation in inhomogeneous media

The earlier phenomenological descriptions of the propagation of signals in inhomogeneous media — except the mirror-type, scattering-type descriptions — have an inherent misunderstanding and therefore these methods are wrong except the non-coupled WKB approximation. The cause of the problem is the wrong physical concept about the structure of the signals propagating in inhomogeneous media. Using a better physical concept of the signal structure propagating in inhomogeneous media and the method of inhomogeneous basic modes (MIBM) it was possible to derive correct full-wave solutions for propagating signals. The investigated example is a monochromatic plane wave propagating in an isotropic, inhomogeneous, linear media parallel to the gradient of the one-dimensional inhomogeneity. However, a generalization of the process for more complex inhomogeneities is possible.

THE LAVOISIER MISSION : A SYSTEM OF DESCENT PROBE AND BALLOON FLOTILLA FOR GEOCHEMICAL INVESTIGATION OF THE DEEP ATMOSPHERE AND SURFACE OF VENUS

Abstract Lavoisier mission is a joint effort of eight European countries and a technological challenge aimed at investigating the lower atmosphere and the surface of Venus. The mission consists of a descent probe and three balloons to be deployed below the cloud deck. Its main scientific objectives may be summarized as following : (i) composition of the deep atmosphere : noble gas (elemental/isotopic), molecular species (elemental/ isotopic), oxygen fugacity; vertical/horizontal/temporal variability; (ii) infrared spectroscopy and radiometry (molecular composition, radiative transfer); (iii) dynamics of the atmosphere : p, T, acceleration measurements, balloon localization through VLBI, meteorological events signed by acoustic waves, atmospheric mixing as imprinted on radioactive tracers; (iv) surface morphology and mineralogy through near infrared imaging on dayside, surface temperature through NIR imaging on nightside. Additional tentative objectives are search for (a) atmospheric electrical activity (optically, radioelectrically, acoustically), (b) crustal outgassing and/or volcanic activity : acoustic activity, horizontal/vertical distribution of radioactive tracers, (c) seismic activity : acoustic waves transmitted from crust to atmosphere, and (d) remanent and/or intrinsic magnetic field. Lavoisier was proposed to ESA in response to the F2/F3 mission Announcement of Opportunity at the beginning of 2000, but it was not selected for the assessment study. A wide international partnership was created for this occasion, including Finland (FMI), France (IPSL, MAGIE, Universite Orsay, IPSN, INPG, CEA, IPGP, Obs. Paris-Meudon), Germany (MPAe, Univ. Muenster), Hungary (KFKI, Univ. Eotvos), Portugal (OAL), Russia (IKI), Spain (IAA), United Kingdom (Univ. Oxford).

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.

Theoretical explanation of the solar limb effect

Abstract The general theory of relativity predicts a wavelength shift of the lines in the solar spectrum with respect to corresponding terrestrial lines by an amount of 2.12 × 10−6. However, it is an established fact that at the extreme solar limb (at radial distances greater than about 95 per cent of the radius of the disk) the Fraunhofer lines exhibit a red-shift substantially exceeding the shift required by the relativity theory (the phenomenon will be referred to as limb effect). On the basis of the general theory of wave propagation in inhomogeneous moving media it is shown that the extreme red-shift values observed at the solar limb are produced by radial currents in the solar atmosphere due to an effect different from the familiar one which is responsible for the wavelength shifts observed at the inner parts of the solar disk.

Whistler-mode propagation: results of model calculations for an inhomogeneous plasma

Waveforms computed using the new whistler model derived from Maxwells equations were analysed. In the calculations, realistic model values for magnetospheric parameters were used. The results accurately described whistler-mode propagation in the magnetosphere and provide explanations for some features exhibited by real observed whistlers when they are analysed. In particular, solutions of the exact full-wave whistler model can explain the whistler fine structure, and may be used to develop a more accurate (matched filtering) fine-structure analysis method.

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%.

A new experimental possibility of investigating the solar corona: Frequency measurements on radio sources when occultated by the Sun

Abstract In the years 1967 and 1968 researchers at the U.S. Naval Research Laboratory reported on an anomalous frequency decrease of the 21 cm radiation of Taurus A when the radio source passed near to the Sun. Up to the present time no satisfactory explanation has been given of the effect. Based on a recently developed general theory of electromagnetic wave propagation, it is shown that the frequency decrease can be attributed to (e.g. electron) particle streams propagating with great velocities in the corona. Further occultational observations would yield an effective method of investigating the solar atmosphere.

Calibration of electron density obtained from whistler inversion with in-situ satellite measurements

Summary form only given. The equatorial electron density obtained from whistler inversion has long been regarded as an effective tool for monitoring the plasmasphere from ground based measurements. However, as these inversion methods are based on various models, it is essential to validate them through comparison with in-situ density measurements. To date, no such comparison was made, mostly because no suitable in-situ was available. Van Allen Probes measure not only the electron density and magnetic field in-situ, but all the six electromagnetic wave components as well allowing a real calibration with whistler-based densities. We have used two approaches for calibration: 1. These six component burst mode measurements are used to find simultaneous satellite and ground based whistler events. Then a partial-path whistler inversion is made to compare the in-situ density with the one derived from whistlers. 2. Equatorial electron densities obtained from ground based whistler events are compared with in-situ electron densities measured at or very close to the equator at the same time. Our recently developed whistler inversion method includes various models, such as wave propagation, magnetic field, field aligned density distribution and equatorial electron density models. The latter one is a special one used for multiple-path whistler groups. We have developed a method for cross calibration of the data from the two sources to validate the models in our whistler inversion method.