Flávio Jorge Ponzoni

In-flight absolute calibration of the Landsat-5 TM on the test site Salar de Uyuni

In Brazil, the increase of the application of quantitative approaches in the natural resources studies using remote sensing technology has required knowledge about the radiometric conditions of remote sensors as the Thematic Mapper (TM) and the Enhanced TM Plus, for instance. The establishment of a correlation between radiometric data and biophysical and geophysical ones has become a frequent need in the Brazilian remote sensing community, and it has increased the demand of calibration coefficients in order to transform digital numbers to physical values like radiance and reflectance. Since the China-Brazil Environmental Remote Sensing Satellite became a reality, the necessity to perform calibration campaigns increased significantly. Following Price and other researchers suggestions, an in-flight absolute calibration of the Landsat-5 data was carried out in the Salar de Uyuni, Bolivia. It was only possible to determine calibration coefficients for bands TM2, TM3, and TM4 due to the saturation of band TM1 and surface moisture conditions that impacted the TM5 and TM7. The methodology applied here seemed to be sufficient to determine valid calibration coefficients for orbital sensors.

Characterization of the Salar de Uyuni for in-orbit satellite calibration

Field work was carried out on June 8 and 9, 1999 to evaluate the use of the Salar de Uyuni as a test site for in-orbit satellite calibration. A dataset of ten Thematic Mapper (TM) images, from 1988-1997, was used to select three test points based on the analysis of the temporal stability of the reflectance of Salars surface. Bidirectional reflectance factor (BRF) values of Salars surface within the precision suitable for vicarious calibration procedures were obtained using a CE313-2/CIMEL radiometer. In spite of seeming visually homogeneous, the BRF values of one test point have presented significative statistical differences with the two others. Atmospheric characterization was possible with a sunphotometer CE317/CIMEL showing the low importance of the atmospheric effects in the image acquisition. The results confirm that the Salar de Uyuni has the characteristics pointed out by many authors as suitable for a vicarious calibration site, specially from April to November because of the reduced rainfall occurrence. The main disadvantages are the difficult access and the critical period for data collecting in the rainy season from November to March. An angular reflectance variation study is recommended in order to evaluate its Lambertian properties.

Análise da dinâmica sazonal e separabilidade espectral de algumas fitofisionomias do cerrado com índices de vegetação dos sensores MODIS/TERRA e AQUA

MODerate-resolution Imaging Spectroradiometer (MODIS) 16-day vegetation index composites with 1 km of spatial resolution from TERRA and AQUA satellites were used to characterize the seasonal dynamics of five Brazilian savanna physiognomies and to analyze their spectral separability in 2004. The Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI), using data from both platforms and from a common set of pixels, were compared to each other. The results showed that: (a) among the physiognomies under study, Dry Forest (Floresta Estacional decidua) presented a marked seasonal dynamics as a result of the leaf fall from the rainy to the dry season (strong decrease in the indices) and of the fast green up of vegetation with precipitation at the end of October (strong and rapid increase in NDVI and EVI values); (b) NDVI showed greater variability between the vegetation classes than EVI only in the dry season; (c) the discrimination between the physiognomies improved from the rainy to the dry season; (d) the NDVI was more efficient than EVI to separate the vegetation classes in the dry season, but the contrary was observed in the rainy season; and (e) for the majority of the dates under analysis, in spite of the variations in the quality of the pixels selected to compose the vegetation index MODIS product and in the Sun-view geometry, no statistically significant differences between the indices generated from both platforms were observed.

Impact of multi-angular CHRIS/PROBA data on their empirical relationships with tropical forest biomass

Images from the Compact High Resolution Imaging Spectrometer (CHRIS), on board the space platform Project for On Board Autonomy (PROBA), were acquired in the Brazilian Amazon region in 62 bands (410–1050 nm) at different view angles. They were evaluated for angular variations in Bidirectional Reflectance Factor (BRF), selected vegetation and anisotropic indices, and their relationship with the Above Ground Biomass (AGB) of some forest successional stages using an empirical approach. Results showed that correlations between AGB and reflectance were influenced by the vegetation anisotropy, which was stronger in the visible than in the near-infrared. The anisotropy increased from the forward (−36°) to the backward (+55°) scattering direction, was greater in the blue and green bands and decreased towards the near-infrared. As a result of this behaviour, several narrow and traditional vegetation indices showed correlation coefficients (R) that varied with view angle. The backscattering–forward scattering contrast, represented by anisotropic indices such as the Normalized Difference Anisotropic Index (NADX) and the Hot spot–Dark spot Normalized Difference Vegetation Index (NDVITD), presented only a small improvement of the relationships with AGB when compared with the performance of the other traditional vegetation indices at nadir viewing.

Estimativa de volume de madeira em plantios de Eucalyptus spp. utilizando dados hiperespectrais e dados topográficos

ABSTRACT – The availability of orbital hyperspectral data has brought new perspectives to both academicand corporative sectors solving demands in forestry science. The main objective of this work was to evaluatethe potential of Hyperion EO-1 hyperspectral data to quantify the biophysical timber volume in Eucalyptus spp stands and the effect of hill shading in that quantification. For this, the correlations between spectraldata and timber volume were performed following the use of Multiple Linear regression models as the descriptorsof the relationships established. The relief effect on the Eucalyptus spp. canopy reflectance was taken intoaccount. The Hyperion EO-1 data were converted to BRF surface values, which were considered the basisof the entire work. The study area was located in the municipality of Capao Bonito (the State of Sao Paulo,Brazil) and included Eucalyptus spp . stands managed by the Votorantim Papel e Celulose company (VCP).Spectral samples were collected in different topographic conditions. In the establishment of the relationshipwith timber volume, the vegetation indices estimated using hyperspectral data resulted in models with higherR2 when considering the topographic illumination effect, showing higher applicability potential of this data.Keywords: Vegetation anisotropy, Biophysical parameters and SRTM.

In-flight absolute calibration of the CBERS-2 CCD sensor data

Since the first images of the sensors on board of CBERS-2 (China-Brazil Earth Resources Satellite) satellite were made available by the National Institute for Space Research (INPE), users have asked information about the conversion of image digital numbers to physical data (radiance or reflectance). This paper describes the main steps that were carried out to calculate the in-flight absolute calibration coefficients for CBERS-2 CCD level 2 (radiometric and geometric correction) images considering the reflectance-based method. Remarks about the preliminary evaluation of these coefficients application are also presented.

Spectral characterization of mangrove leaves in the Brazilian Amazonian Coast: Turiaçu Bay, Maranhão State

Mangrove communities are tropical systems which have fewer species than tropical forests, especially in Latin America and display a single architecture, usually lacking the various strata commonly found in other forest ecosystems. The identification of mangrove communities by orbital data is not a difficult task but the most interesting challenge is to identify themselves by the dominant species. The first step toward that floristic identification is the spectral characterization of detached leaves. Leaves from four species of mangrove trees were spectrally characterized considering the Directional Hemispherical Reflectance Factor (DHRF) determined through radiometric measurements using an integrating sphere LICOR 1800 attached to a spectroradiometer SPECTRON SE-590. In the visible bands (0.45-0.69 microm) the button-shaped mangrove Conocarpus erectus was brighter and the red mangrove Rhizophora mangle was darker than the other two species which shows very close DHRF values. Otherwise the black mangrove Avicennia germinans and the white mangrove Laguncularia racemosa can be distinguished from one another in the Near Infra Red (NIR) region (0.76-0.90 microm and in this region of the spectrum the DHRF of C. erectus and R. mangle become very close.

In-flight absolute calibration of the CBERS-2 IRMSS sensor data

Since the first images from the sensors onboard CBERS‐2 (China–Brazil Earth Resources Satellite) were made available by the National Institute for Space Research (INPE), users have requested information about the conversion of image digital numbers into physical data (radiance or reflectance). This Letter describes the main steps that were carried out to calculate the in‐flight absolute calibration coefficients for CBERS‐2 Infrared Multispectral Scanner (IRMSS) level 2 (radiometric and geometric correction) images considering the reflectance‐based method. Remarks about the preliminary evaluation of the application of these coefficients are also presented.

Spectral and Atmospheric Characterization of a Site at Atacama Desert for Earth Observation Sensor Calibration

The application of Earth observation sensor data in quantitative approaches calls on the conversion of original digital numbers to radiometric quantities such as radiance or reflectance. This conversion depends on the sensor absolute calibration. One of the postlaunch methods adopted to calibrate orbital sensors is the reflectance-based approach. According to this method, a reference surface with specifics characteristics is required. The main objective of this work is to evaluate the suitability of a specific surface located at Atacama Desert in Chile to be used as a reference surface for calibration of Earth observation sensor purposes. A field campaign was carried out from August 19 to 22, 2014, when radiometric measurements were performed to spectrally characterize the reference surface and to evaluate the atmospheric characteristics of the study area. The average reference surface reflectance factor in the spectral region from 350 to 2500 nm ranged from 0.1 to 0.3, and its spatial uniformity was within 2%-4%. The amount of atmospheric aerosols was low, with an aerosol optical depth at 550 nm between 0.08 and 0.11 during the fieldwork period. The climate is hyperarid, and the water column abundance was lower than 0.43 g/cm2. The results demonstrated that a reference surface at Atacama Desert could be effectively used for calibration of either airborne or orbital electrooptical sensors, providing an excellent surface in South America.

CARACTERIZAÇÃO ESPECTRO-TEMPORAL DE DOSSÉIS DE Eucalyptus spp. MEDIANTE DADOS RADIOMÉTRICOS TM/Landsat5

TM/Landsat 5 images (April and May 2009) from Capao Bonito (SP) region where Eucalyptus urophilla, Eucalyptus grandis and a hybrid of both species have been planted were utilized in the spectral characterization of some stands that presented structural differences explained mainly by age. These images have been converted to physical values such as surface reflectance factors and from these values principal components images were generated. The dispersion of PC1 and PC2 on a bi-dimensional space has been evaluated to identify tendencies of pixels positioning. Results have shown that for young eucalyptus canopies (up to 3 years old) the positioning is well defined, occupying the lower part of the dispersion clouds and far from the graph origin (zero). This result indicates more participation of the lower portions of the canopies, which presents lower values of reflectance in the near infrared (bare soil or dry branches) and high reflectance in the visible region. The older canopies presented higher influence of photosynthetic active leaves rather than the shadowed and lower portions of the canopies. The spectral characterization of eucalyptus canopies at the two temporal set of data was consistent.