Fernando Rull Pérez

Digital metric camera radiometric and colorimetric calibration with simultaneous CASI imagery to a CIE standard observer based colour space

The Institut Cartografic de Catalunya (ICC) operates a digital metric camera (DMC), manufactured by Z/Imaging. It supports the simultaneous capture of panchromatic, RGB colour and near-infrared images. One of the most important ICC products is the Catalonia orthophotomap series. This product is intended to depict the territory as realistically as possible. With this aim, ICC is developing a project to obtain genuine colours in the photographic products produced with the DMC camera and this paper contains some preliminary results. Since an absolute radiometric calibration of the DMC is not available yet, this is accomplished through simultaneous images acquired with both DMC and a compact airborne spectral imager (CASI) also operated by ICC. These images are used to locate common areas imaged in similar geometrical conditions, and then a linear relationship between digital numbers (DN) from DMC and radiance values of a CASI image emulating DMC bands is calculated. To improve the colour of the DMC products, a colorimetric calibration based on polynomial transformations has been developed. This transformation allows changing from DMC-RGB space to a sRGB space that is based on CIE-XYZ colour space. Airborne ICC-CASI images acquired with a Cessna Caravan B20 over Banyoles (Spain) in 2005 were used to test the methodology. The comparison between the training colours and the ones obtained after colorimetric calibration yield differences in 8 bit DN that range from 4 to 36 DN with a mean value of 12 DN. The effect was also visually analyzed on different subsets of images that include agriculture areas, urban landscape and a natural water layer. Finally, it was found that the application of both calibrations to the DMC images results in a consistent colour combinations for all the analyzed subsets.

Development of a multiple adjustment processor for generation of DEMs over large areas using SAR data

During the last years orbital SAR data have been acquired for almost every place in the world. This fact can be used for generating large digital elevation models (DEM) of remote areas using SAR interferometry (InSAR). Nevertheless, the generation of large quality DEMs using this technique presents several problems, such as temporal decorrelation (even with a one-day temporal gap between acquisitions), baseline errors or SAR parameters calibration. These factors can dramatically degrade the quality of the final DEM and, therefore, advanced InSAR techniques are needed to minimize or compensate for these errors. In this paper the Institut Cartogra/spl grave/fic de Catalunya (ICC) presents a robust method for generating very large, high quality DEMs using a set of SAR interferograms. The method is based on a simultaneous multiple adjustment of critical parameters for the SAR images using three types of phase-registered points: control points, known-height and corresponding points. Results for the area of Tierra del Fuego (Argentina) are also presented.

Simultaneous usage of optic and thermal hyperspectral sensors for crop water stress characterization

Visible-Near InfraRed (VNIR) and Thermal InfraRed (TIR) simultaneous information is crucial in order to carry out a reliable description of crop water stress condition. In this paper, a study based on the hyperspectral sensors TASI and CASI, which are regularly operated by the Institut Cartogràfic de Catalunya (ICC) since 2009, is proposed. High-resolution hyperspectral data sets acquired over a vineyard in Raïmat (Spain) are employed to characterize the energy flux exchange between surface and atmosphere, and to estimate the crop daily evapotranspiration (ETd). Finally, a relative Crop Water Stress Index (CWSI) is obtained under specific assumptions upon the water stress condition of reference plants within the imaged scene.

Reducing systematic errors on SMOS retrieved salinity: Calibration of brightness temperature images and forward model improvement

SMOS salinity inversion consists of minimizing the residual between measured and modeled brightness temperatures. The minimization procedure is a great challenge and crucial step, but its success depends on the quality of the forward model. Consequently, we present an empirical update of pre-launch L-band emissivity forward models, where the essential improvement is related to the emissivity by a rough sea surface. The improvement is quantified in terms of retrieved salinity accuracy compared to the climatology.

A methodology for luminance map retrieval using airborne hyperspectral and photogrammetric data

This paper puts forward a methodology developed at the Institut Cartogràfic i Geològic de Catalunya (ICGC) to quantify upwelling light flux using hyperspectral and photogrammetric airborne data. The work was carried out in the frame of a demonstrative study requested by the municipality of Sant Cugat del Vallès, in the vicinity of Barcelona (Spain), and aimed to envisage a new approach to assess artificial lighting policies and actions as alternative to field campaigns. Hyperspectral and high resolution multispectral/panchromatic data were acquired simultaneously over urban areas. In order to avoid moon light contributions, data were acquired during the first days of new moon phase. Hyperspectral data were radiometrically calibrated. Then, National Center for Environmental Prediction (NCEP) atmospheric profiles were employed to estimate the actual Column Water Vapor (CWV) to be passed to ModTran5.0 for the atmospheric transmissivity τ calculation. At-the-ground radiance was finally integrated using the photopic sensitivity curve to generate a luminance map (cdm-2) of the flown area by mosaicking the different flight tracks. In an attempt to improve the spatial resolution and enhance the dynamic range of the luminance map, a sensor-fusion strategy was finally looked into. DMC Photogrammetric data acquired simultaneously to hyperspectral information were converted into at-the-ground radiance and upscaled to CASI spatial resolution. High-resolution (HR) luminance maps with enhanced dynamic range were finally generated by linearly fitting up-scaled DMC mosaics to the CASI-based luminance information. In the end, a preliminary assessment of the methodology is carried out using non-simultaneous in-situ measurements.

Radiometric characterisation of a VNIR hyperspectral imaging system for accurate atmospheric correction

The Institut Cartogàfic de Catalunya (ICC) regularly operates a Compact Airborne Spectral Imager (CASI) sensor. For this system an atmospheric correction algorithm was developed to simultaneously correct multiple overlapping images taken from different heights. First, the algorithm estimates the main atmospheric parameters with an inversion procedure using either radiometric ground measurements or image homologous areas plus a single ground measurement. Then, the code is applied to the images to obtain atmospherically corrected hyperspectral imagery. The algorithm was applied in the frame of ICC-Banyoles 2005 experiment (Spain) using multi-height imagery and field simultaneous reflectance measurements. In the validation step, the standard deviations obtained with both inversion methods were similar. In order to improve these results, the smiling effect (spectral shift) for the sensor is characterized by locating O2 absorption bands in the NIR for each CASI look direction. Additionally, a more accurate spectral sensitivity for each band has been calculated. These improvements are applied to EuroSDR-Banyoles 2008 experiments (Spain) imagery. These results show a substantial improvement on the atmospheric correction at the absorption regions when compared to field reflectance measurements. This behaviour advises the inclusion of these developments in the inversion system.

Raman spectroscopic analysis of an important Visigothic historiated manuscript

Raman spectroscopy has been used to study fragments of early Visigothic historiated manuscripts from the important mediaeval library at Santo Domingo de Silos which were a part of a Beato dating from the tenth to the mid-eleventh centuries. These fragments are from some of the oldest manuscripts in the scriptorium of the monastery. In this study, a comparison is made between the pigments and inks used on these manuscripts and those used in a previous study of the unique Visigothic Beato de Valcavado in Santa Cruz, Valladolid, completed in the year 970, which is noted for its quality of execution as well as its content and is remarkable eschatologically in being identifiable as the complete work of only a single scribe. For comparative purposes, the pigments and inks used in the Silos Monastery Beato and a series of historiated early manuscripts from mediaeval times through to the Renaissance also held in the monastic library were analysed. Raman spectroscopy identified a range of mineral and organic pigments such as cinnabar, orpiment, minium, azurite and indigo. In addition, a number of admixtures were found, for example, indigo and orpiment to produce vergaut (green) and a mixture of cinnabar with iron-gall ink and cerussite to produce darker and lighter shades of red. Some interesting conclusions were drawn about the use of iron-gall and carbon-based inks. This article is part of the themed issue ‘Raman spectroscopy in art and archaeology’.

Automatic Raman Spectra Processing for Exomars

Our process of automatic identification of Raman spectra includes algorithmics and mathematical methods, and it is divided in two main steps. The first one consists on the pre-processing of the spectra. This includes reducing the spectral noise level by means of smoothing filters with adjustable parameters which depend on the spectral characteristics of the data. In addition, it is necessary to remove the baseline of the spectra, as a curved baseline can hinder the processing of relevant spectral data. To do so, several different approaches and mathematical methods have been studied, and a new method has been proposed. Finally, a method has been developed to provide robust and autonomous peak detection based on the specific characteristics of the spectrum. The second step consists on the automatic ID of spectra. For this, an algorithm which compares band positions and intensities has been implemented to decide what materials are present in the spectrum under study.

Aerial photography restoration using the maximum likelihood estimator (MLE) algorithm

We apply the maximum likelihood estimator (MLE) method to restore scanned photogrammetric plates. In color images, the restoration is carried out separately for each band. To compute the MLE solution, we use the algorithm based on the expectation maximization (EM) algorithm for Poisson data. The memory and CPU time needed to obtain MLE solutions make feasible the restoration of images of 512 X 512 or 1024 X 1024 pixels, but the restoration of a series of large scanned photographs, as happens with photogrammetric plates, is not of practical use with present-day computers. With the aim of bypassing this problem, several 512 X 512 portions of the plate are extracted and restored with the MLE algorithm. Then, the convolution function transforming the original into the restored image is calculated in Fourier space, thus obtaining a convolution matrix when returning to normal space. Next, this matrix is truncated and a convolution is performed over the whole image. A series of tests over the same image digitized with different scanners has been carried out to separate this contribution from environmental effects.

New SMOS salinity products at CP34-BEC in Barcelona

New ocean products from the Soil Moisture and Ocean Salinity (SMOS) mission are being developed at the Barcelona Expert Centre. Besides the already operational 9-day and monthly sea surface salinity (SSS) products, two additional daily SSS products have been recently become operational: a simple user-friendly product containing all swath-based Level 2 data for each day, and a more elaborated product that uses multifractal fusion techniques to increase the spatial and temporal resolution. Finally, experimental BEC products are also presented which provide SSS values in regions strongly affected by radio-frequency interference (RFI). Recent progress on Land-Sea contamination mitigation has been applied to the BEC products.