CENTIMETER COSMO-SKYMED RANGE MEASUREMENTS FOR MONITORING GROUND DISPLACEMENTS

The SAR (Synthetic Aperture Radar) imagery are widely used in order to monitor displacements impacting the Earth surface and infrastructures. The main remote sensing technique to extract sub-centimeter information from SAR imagery is the Differential SAR Interferometry (DInSAR), based on the phase information only. However, it is well known that DInSAR technique may suffer for lack of coherence among the considered stack of images. New Earth observation SAR satellite sensors, as COSMO-SkyMed, TerraSAR-X, and the coming PAZ, can acquire imagery with high amplitude resolutions too, up to few decimeters. Thanks to this feature, and to the on board dual frequency GPS receivers, allowing orbits determination with an accuracy at few centimetres level, the it was proven by different groups that TerraSAR-X imagery offer the capability to achieve, in a global reference frame, 3D positioning accuracies in the decimeter range and even better just exploiting the slant-range measurements coming from the amplitude information, provided proper corrections of all the involved geophysical phenomena are carefully applied. The core of this work is to test this methodology on COSMO-SkyMed data acquired over the Corvara area (Bolzano – Northern Italy), where, currently, a landslide with relevant yearly displacements, up to decimeters, is monitored, using GPS survey and DInSAR technique. The leading idea is to measure the distance between the satellite and a well identifiable natural or artificial Persistent Scatterer (PS), taking in account the signal propagation delays through the troposphere and ionosphere and filtering out the known geophysical effects that induce periodic and secular ground displacements. The preliminary results here presented and discussed indicate that COSMO-SkyMed Himage imagery appear able to guarantee a displacements monitoring with an accuracy of few centimetres using only the amplitude data, provided few (at least one) stable PS's are available around the monitored area, in order to correct residual biases, likely due to orbit errors

Sensitivity of the WorldView-2 satellite orthoimage horizontal accuracy with respect to sensor orientation method, number and distribution of ground control points, satellite off-nadir angles and strip length

Imagery acquired by the WorldView-2 (WV2) sensor is of potential interest to the Control with Remote Sensing (CwRS) Programme of the European Commission and therefore needs to be assessed. In details, the horizontal accuracy of the orthoimages which can be derived from WV2 imagery have to be concerned, recalling that in order to qualify WV2 as a Very High Resolution (VHR) prime sensor (i.e. a sensor suitable for measuring parcel areas to the accuracy requested by the Common Agriculture Policy - CAP regulation), the CwRS guidelines requires that the one-dimensional RMSE error (i.e. in the East and North components) measured on the external Check Points - CPs for any orthoimage should not exceed 2.5 m. This report summarizes the results regarding the orientation tests of the five WorldView-2 Panchromatic (WV2 PAN) images acquired over the JRC Maussane Test Site (Provence, Southern France), two Pan-sharpened (WV2 PANSHP) images (COSE_MODE_1) acquired over Cosenza Test Site (Southern Italy) and 9 Pan-sharpned (WV2 PANSHP) scenes (COSE_MODE_3) acquired over Cosenza Test Site (Southern Italy), carried out with Geomatica (PCI Geomatics), ERDAS Imagine 2011 and SISAR software, using both Rigorous model and Rational Polynomial Functions (RPFs) model with Rational Polynomial Coefficients (RPCs). The Hold-Out-Validation accuracy assessment method (HOV) was considered, computing the Root Mean Square Error (RMSE) of the residuals between the estimated and the reference positions of the Check Points (CPs) for each horizontal component (East, North) varying the number of the GCPs. In addition the Leave-One-Out Cross Validation (LOOCV) method was been used to identify possible outliers.JRC.H.4-Monitoring Agricultural Resource

Precipitable water vapour content from ESR/SKYNET sun-sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

The estimation of the precipitable water vapour content (W) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun-sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W, from independent sources, taken over a large range of solar zenith angle and covering a wide range of W, are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8% in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8% in the case of AERONET comparison in Valencia. Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of %bias, bringing the agreement with the GPS (considered the reference one) from a %bias of 5.76 to 0.52

DEM Extraction from high resolution satellite stereo pairs to investigate the hydraulic hazard of area subjected to rivers flood

As far as the monitoring of the hydraulic hazard of flat areas is concerned, a very important role is played by studies concerning the outflow of water after river floods or downpours. Such studies are based on complex forecasting hydraulic models, which need an accurate and detailed DSM as input together with planimetric and altimetric data regarding all the natural and anthropic objects, as riverbanks or roads in relief, which may interfere with the outflow of water. The aim of this work is the evaluation of DSMs extracted from high resolution stereo pairs for their application in hydraulic hazard analysis. The advantages arising from the use of satellite images are mainly relative low costs and fast elaboration. The investigation has been carried out on an in-track Ikonos stereopair acquired over the area of the town of Ferrara (Northeastern Italy, near the Po delta) on July 2004. The best workflow to generate the DSM has been evaluated: the orientation has been performed both with the commercial software PCI Geomatics OrthoEngine v10.2 and with the scientific software SISAR, developed by La Sapienza University of Rome. Image matching and DSM extraction have been performed with PCI Geomatics and SISAR matching facility but also, for the image matching, with the scientific software DPCOR, developed by Leibniz University of Hannover. The DSM accuracy has been evaluated comparing a reference DSM derived from a recent photogrammetric flight with all the extracted DSMs