Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites

The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites was investigated. Co2+ ions are known to lead to a compensation of the magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on the cobalt content and the Ni/Zn ratio. We observed similar behaviour in Ni-Zn-Cu and it was found that the core loss goes through a minimum around this magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced by the cobalt allowed a strong decrease of core loss, a ferrite having a core loss of 350 mW/cm3 at 80 ^\circ C was then developed (measured at 1.5 MHz and 25 mT). This result represents an improvement of a factor 4 compared to the state of art Ni-Zn ferrites

Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites

Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites, initial complex permeability was then measured from 1 MHz to 1 GHz. It appears that cobalt substitution led to a decrease in the permeability and an increase in the \mus\timesfr factor. As well, it gave to the permeability spectrum a sharp resonance character. We also observed a spin reorientation occurring at a temperature depending on the cobalt content. Study of the complex permeability versus temperature highlighted that the most resonant character was obtained at this temperature. This shows that cobalt contribution to second order magnetocrystalline anisotropy plays a leading role at this temperature

An operational solution to acquire multispectral images with standard light cameras : Characterization and acquisition guidelines

In order to develop a low-cost and easy to implement technical solution to map inside-field spatial variability, and to explore its relationship with crop conditions, several experiments were conducted using ultra-light aircraft and Unmanned Aerial Vehicle (UAV) equipped with visible and infrared cameras. The sensors consisted of a ramp of 3 small format digital cameras (EOS 350D, Canon®): one for the visible part of the spectrum, and two modified cameras in order to acquire red edge and near infrared radiations. The images acquisition on the 3 cameras is simultaneous using external triggers and can be activated through the operator remote control on the ground or programmed to be automatically done using an on-board GPS navigation system. On ultra-light aircraft we also add a microbolometer thermal camera to the system. This paper describes the components of this acquisition system and focuses on the geometric and radiometric processing steps necessary for quantitative use of the data. At an altitude of 500 m this system acquires images with a ground resolution of 8 cm for the visible and near infrared bands and 55 cm for the thermal band. Unmanned Aerial Vehicle common altitude stretches over several tenth of meters up to 500 m and is adapted to the survey of fields of several hectares with very high spatial resolution. Ultra-light aircraft offers a range of altitude up to 1 to 2 km and a larger survey capacity with smaller spatial resolution. The spectral sensitivity of the cameras was measured using monospectral emittance sources. We worked both on the raw multispectral images and on the computed jpeg standard output. This allowed us to select the best band (or band combination) to produce red edge and near infrared images. We also developed an algorithm to compensate some radiometric distortion in the acquired images, particularly on vignetting effect. Classical photogrammetric calibration was used in order to measure lens geometry of each camera and evaluate as precisely as possible the coefficients of the lens polynom needed by commercial photogrammetric software. Several sets of images were acquired over experimental fields in temperate zone (on wheat) and tropical zone (on sugarcane). These images were radiometrically and geometrically corrected used the above elements and are stored as georeferenced stackable images in a Geographic Information System. The next step for a quantitative use of the data is to compensate changes due to atmospheric and illumination conditions in the image time series. (Résumé d'auteur

Recalibrating a sugarcane crop model using thermal infrared data

Coupling remotely sensed data with crop model is known to improve the estimation of crop variables by the model. The recalibration coupling approach tends to reduce the differences between observation and simulation by optimizing the value of one of the model's parameter. In this study, we used this approach with a sugarcane model and Crop Water Stress Index calculated using remotely sensed thermal infrared data in order to optimize the value of the root depth parameter thanks to measured and simulated AET/MET ratio. The effect of the root depth recalibration has also been assessed on the yield estimation, which showed good trends with a significant enhancement of the estimated yield. (Résumé d'auteur

Sensitivity of airborne-derived crop stress indices to the agricultural practices

When acquired both in optical and thermal infrared domain, remotely sensed data can provide a wide range of information about the status of a crop. Several studies have demonstrated the utility of such information for the development of stress indices that can be related to water, nitrogen or global physiological status of the plant. In this paper, we investigate the relationships between crop biophysical parameters (LAI, SPAD, Humidity) and two airborne-derived spectral indices (NDVI: Normalized Vegetation Index, and CSI: Crop Stress Index) under different agricultural practices in terms of water treatment, nitrogen input and cultivar for sugarcane crop. We then discuss of the potentialities of the combined use of these two indices for a better understanding of crop status. (Résumé d'auteur

The compilatory nature of the 126 manuscript of Archivo Capitular de El Burgo de Osma

En este trabajo se aborda el estudio de aquellos aspectos que nos llevan a considerar al ms. 126 del Archivo Capitular de El Burgo de Osma un códice compilatorio: por una parte, la identificación de las fuentes de las que beben dos de sus glosas de contenido mitológico y, por otra, el análisis de la estructura del códice en su conjunto y de la relación entre las obras que lo componen.In this paper I study those aspect that lead us to consider the ms. 126 of Archivo Capitular de El Burgo de Osma a compilatory codex: on the one hand, I will identify the sources of two glosses with mythological nature and, on the other, I will analize the structure of the whole codex and the link between its literary works

Radiometric normalization of multi-temporal visible and near infrared images acquired with light ariborne systems

To study the structure and dynamics of environmental targets, light airborne systems are more and more used as a complement to usual satellite or aerial acquisitions. These systems are composed of small-format digital frame cameras mounted on an ultralight aircraft or an unmanned aerial vehicle. Standard and modified cameras measure the reflected radiation in the visible, the red-edge and near-anfrared bands. The whole system and the geometric and radiometric pre-processing of the images are described in details in the paper "An operational solution to acquire multispectral images with standard light cameras: spectral characterization and acquisition guidelines" submitted for approval to this symposium. This paper deals with the radiometric processing of images time series. Multiple images of the same region captured under different conditions are difficult to compare. This is due to changes in illumination, atmospheric conditions, and flight parameters. Without radiometric normalization, changes between two images are difficult to interpret: they can be linked either to real changes of the surface or to non-scene-dependent changes. In this paper, we propose to compare three methods of radiometric normalization: The invariant targets: - This method consists in uniformly minimizing the effects of non-scene-dependent changes according to a reference date. A given date (image) is chosen as a reference and linear regressions are established, for each of the spectral band between the digital count of invariant points at this date and at all other dates. These linear regressions are then applied to the whole images to normalize them relatively to the reference image. - The spectral indices: ratio-based indices are calculated using the digital counts. This type of indices normalizes by construction the incident radiation. - The calculation of the incident radiation: we use an atmospheric radiative transfer model to calculate the incident radiation at the Top Of the Canopy (TOC) in each spectral band. The model atmospheric inputs come either from meteorological measurements (visibility) or from mean climatic values (water content). The incident radiation values are then used to normalize the digital counts for each acquisition date. In order to evaluate the sensitivity of the model to the accuracy of the atmospheric inputs, a sensitivity analysis will be first performed. The methods will be compared using a time set of airborne multispectral images (blue, green, red, red-edge and near-infrared bands) acquired over agricultural land on Reunion Island. (Texte intégral

Improving harvest and planting monitoring for smallholders with geospatial technology: the Reunion Island experience

8 pagesInternational audienceWith the recent development of geospatial technologies, remote sensing data are more and more integrated in the information systems of crop industries. The satellite's ability to collect "snapshots" over large cropped areas at once makes it a unique tool to able it to acquire localized and objective data in real-time.In this paper, we present how this technology can provide reliable information for sugarcane planting and harvest monitoring by updating information on field/blocks boundaries and cane status using time series of satellite images. Through the experience conducted on Reunion Island (Indian Ocean) where the sugar industry has difficulty collecting updated localized information on smallholders fields, we show how SPOT satellite images can be interpreted and processed in order to produce thematic maps and statistics. These maps can then be integrated in a Geographic Information System (GIS) designed for decision makers. This on-the-shelf GIS permits one to visualize maps and edit monthly statistics of the management practices in each production area