Mauro Antonio Homem Antunes

Distribuição espacial de pivôs centrais no Brasil: I - região sudeste

Irrigated areas by state and by irrigation method is the available information about irrigation in Brazil. Distribution inside the states, number or size is not easily found even through the industry. These data are very important when one intends to study water availability or growth potencial of irrigated areas for a specific site due to the increasing concern about drinking water worldwide and nationally. The present study had the objective to collect such information using satellite images from Landsat based on the intrinsic characteristic of the center pivot equipments, the circular mark on landscape easily visible. With comparison the geo-referenced images and its articulation with the official IBGE maps, it was possible to draw the state maps with the equipment density distribution, which, when compared to other available sources permitted to validate the methodology used for this purpose.

Atmospheric effects on vegetation indices of TM and ETM+ images from a tropical region using the 6S model

Vegetation indices have been widely used for monitoring vegetation and to estimate vegetation biophysical parameters. The atmosphere affects differently sensor bands depending on the waveband, thus affecting the indices obtained from top of the atmosphere reflectances. The objective of this paper is to evaluate the atmospheric effects on the NDVI and SAVI using the 6S model adapted for atmospheric correction of images of eight bits digital numbers. Images from the TM and ETM+ sensors of the same area were corrected for the atmosphere and the vegetation indices were compared with those from noncorrected images. For these images the results show that the vegetation indices at the top of the atmosphere were lower than those from the surface. This underestimation of the vegetation indices due to the atmosphere is attributed to a higher absorption of radiation in the near infrared than in the red spectral region. This is exceptionally pronounced on tropical atmospheres where absorption by water vapor tends to be higher than in mid-latitudes. It is concluded that atmospheric correction is necessary when calculating vegetation indices over tropical regions and the adapted 6S model is suitable for this task.

Ocorrência de veranicos no estado do Rio de Janeiro

The objective of this work was to simulate droughts with different duration ranges (1-5, 6-10 and 11-15 days) in order to identify its occurrence probability in Rio de Janeiro State, Brazil, between December to February. Rain gauge data collected over 16 years from 62 weather stations, 40 from Rio de Janeiro, 15 from Minas Gerais, 4 from Espirito Santo and 3 from Sao Paulo, were used in the analysis. The results allowed the conclusion that, in general, the highest drought probabilities were found for December, decreasing in January and from January to February. Drought periods lasting 1-5 and 6-10 days were found to occur with greater probability in the State. The probability of droughts lasting 11-15 days was higher in Northern region, particularly in February. The Southern State region presented higher probability of droughts for periods of 1-5 days.

Relação entre dados de sensoriamento remoto e perdas de solo em entressulcos observadas em campo

The objective of this work was to evaluate the relationship between different remote sensing data, derived from satellite images, and interrill soil losses obtained in the field by using a portable rainfall simulator. The study was carried out in an area of a hydrographic basin, located in Médio Paraíba do Sul, in the state of Rio de Janeiro – one of the regions most affected by water erosion in Brazil. Evaluations were performed for different vegetation indices (NDVI, Savi, EVI, and EVI2) and fraction images (FI), derived from linear spectral mixture analysis (LSMA), obtained from RapidEye, Sentinel2A, and Landsat 8 OLI images. Vegetation indices are more adequate to predict soil loss than FI, highlighting EVI2, whose exponential model showed R2 of 0.74. The best prediction models are generated from the RapidEye image, which shows the highest spatial resolution among the sensors evaluated.

OLI image atmospheric correction sensitivity to altitude, visibility and acquisition geometry

Atmospheric effects can damage surface information extraction from satellite images and correction using physically based models is a way to minimize these effects. This paper presents a sensitivity analysis of atmospheric correction of an OLI image using a base case from which the surface altitude, horizontal visibility and viewing geometry were varied. Results show that viewing geometry, target altitude and horizontal visibility affects the ground reflectance retrieval, mainly in the visible bands. Atmospheric effects decreased from the backscattering to the forward scattering while it decreased as target altitude increased. It is concluded that the use of average values of these correction parameters can be a problem when performing the atmospheric correction. It is recommended that care should be taken when using average values and preferably use correction that takes into account the within image variations of these parameters.

Land cover variation of Minnaert constant for topographic correction of thematic mapper data

Topography affects the surface radiation distribution thus restricting the extraction of thematic information from orbital data. Many models have been proposed to minimize this problem, including the Minnaert model. The variation of Minnaerts constant - k - was investigated for a tropical region with extreme differences of land cover. A TM Landsat 5 image along with a DEM produced from a contour map at a 1:50,000 scale were used. The results for forest and non-forest areas showed increase on k values from TM1 to TM7 bands as found in the literature. The differences between classes that uses a unique k value in the entire image need to be avoided.