Wet Refractivity tomographic reconstruction over small areas using an ad-hoc GPS receivers network

One of the most attractive scientific issues in the use of GNSS (Global Navigation Satellite System) signal from a meteorological point of view, is the retrieval of high resolution tropospheric water vapour maps. The real-time (or quasi real-time) knowledge of such distributions could be very useful for several applications, from operative meteorology to atmospheric modeling. Moreover, the exploitation of wet refractivity field reconstruction techniques can be used for atmospheric delay compensation purposes and, as a very promising activity, it could be applied for example to calibrate SAR or Interferometric-SAR (In-SAR) observations for land remote sensing. This is in fact one of the objectives of the European Space Agency project METAWAVE (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water vapour Effects), in which several techniques were investigated and results were compared to identify a strategy to remove the contribution of water vapour induced propagation delays in In-SAR products. Within this project, the tomographic reconstruction of three dimensional wet refractivity fields on a small atmospheric volume (16km x 20 km x 10 km height, from 2 km to 4 km horizontal resolution and 1 km vertical resolution), was performed considering real tropospheric delays observations acquired by a GNSS network (9 dual frequency GPS receivers) deployed over Como area (Italy), during 12-18 October, 2008. Acquired L1 and L2 carrier phase observations have been processed in terms of hourly averaged Zenith Wet Delays. These vertical informations have been mapped along the correspondent line of sights (by up-sampling at 30 second sample times the 15 minutes GPS satellites positions obtained from IGS files) and inverted using a tomographic procedure. The used algorithm performs a first reconstruction (namely, the tomographic pre-processing) based on generalized inversion mechanisms, in order to define a low resolution first guess for the following step. This second step inverts GPS observables using a more refined algebraic tomographic reconstruction algorithm, in order to improve both vertical and horizontal resolution. Despite limitations due to the network design, internal consistency tests prove the efficiency of the adopted tomographic approach: the rms of the difference between reconstructed and GNSS observed Zenith Wet Delays (ZWD) are in the order of 4 mm. A good agreement is also observed between our ZWDs and corresponding delays obtained by vertically integrating independent wet refractivity fields, taken by co-located meteorological analysis. Finally, during the observing period, reconstructed vertical wet refractivity profiles evolution reveals water vapour variations induced by simple cloud covering. Even if our main goal was to demonstrate the effectiveness in adopting tomographic reconstruction procedures for the evaluation of propagation delays inside water vapour fields, the actual water vapour vertical variability and its evolution with time is well reproduced, demonstrating also the effectiveness of the inferred 3D wet refractivity fields. Even if results obtained were satisfactory, limitations due to the observation geometry, to the GNSS propagation delay information extraction form observables and to the applied tomographic technique will be highlighted, in order to trace the road-map toward future improvements in this challenging fiel

Constellation of cubesats: 3-star in the humsat/geoid mission

The 3-STAR program is the new cubesat educational project at the Politecnico di Torino. It has been thought in response to the GEOID call for proposals issued by the Education Office of the European Space Agency. The GEOID (GENSO Experimental Orbital Initial Demonstration) initiative wants to settle an orbiting constellation of cubesats to be operated by the GENSO (Global Educational Network for Satellite Operations) ground-stations network. GEOID is expected to be the communication backbone of the initial version of the HUMSAT system. The main goal of HUMSAT is to use the constellation of satellites and the GENSO ground stations, to provide support for humanitarian initiatives, especially in developing areas or areas without infrastructure. The 3-STAR will be one of the nine cubesats in the GEOID constellation. It will be a 3U cubesat derived from the e-st@r cubesat experience. In addition, it will carry two payloads: the HumSat payload, consisting of a simple but extremely reliable communication module compatible with the elements of the HUMSAT system, and the P-GRESSION (Payload for GNSS remote sensing and signal detection) payload. The P-GRESSION payload aims at performing measurements by means of radio-occultation technique and scattering theory, using GNSS signals. In this paper the 3-STAR project is described together with a preliminary assessment on the performances of the GEOID/HUMSAT constellation. The main requirements of the GEOID/HUMSAT project have been used to drive an optimization process aimed at determining the best configurations of a swarm-like constellation of cubesats. The mission scenario is made of the nine GEOID cubesats, a number of GENSO ground nodes and several sensors distributed on the Earth surface. The results of the analysis demonstrate that the aspects related to the cubesat-system design cannot be decoupled from the design of the constellation, not even in a preliminary phase. Further, it is demonstrated that the performances of a swarm-like constellation are comparable to those of a well-distributed on

Constellation of cubesats: 3-star in the humsat/geoid mission

The 3-STAR program is the new cubesat educational project at the Politecnico di Torino. It has been thought in response to the GEOID call for proposals issued by the Education Office of the European Space Agency. The GEOID (GENSO Experimental Orbital Initial Demonstration) initiative wants to settle an orbiting constellation of cubesats to be operated by the GENSO (Global Educational Network for Satellite Operations) ground-stations network. GEOID is expected to be the communication backbone of the initial version of the HUMSAT system. The main goal of HUMSAT is to use the constellation of satellites and the GENSO ground stations, to provide support for humanitarian initiatives, especially in developing areas or areas without infrastructure. The 3-STAR will be one of the nine cubesats in the GEOID constellation. It will be a 3U cubesat derived from the e-st@r cubesat experience. In addition, it will carry two payloads: the HumSat payload, consisting of a simple but extremely reliable communication module compatible with the elements of the HUMSAT system, and the P-GRESSION (Payload for GNSS remote sensing and signal detection) payload. The P-GRESSION payload aims at performing measurements by means of radio-occultation technique and scattering theory, using GNSS signals. In this paper the 3-STAR project is described together with a preliminary assessment on the performances of the GEOID/HUMSAT constellation. The main requirements of the GEOID/HUMSAT project have been used to drive an optimization process aimed at determining the best configurations of a swarm-like constellation of cubesats. The mission scenario is made of the nine GEOID cubesats, a number of GENSO ground nodes and several sensors distributed on the Earth surface. The results of the analysis demonstrate that the aspects related to the cubesat-system design cannot be decoupled from the design of the constellation, not even in a preliminary phase. Further, it is demonstrated that the performances of a swarm-like constellation are comparable to those of a well-distributed on

Data intensive scientific analysis with grid computing

At the end of September 2009, a new Italian GPS receiver for radio occultation was launched from the Satish Dhawan Space Center (Sriharikota, India) on the Indian Remote Sensing OCEANSAT-2 satellite. The Italian Space Agency has established a set of Italian universities and research centers to implement the overall processing radio occultation chain. After a brief description of the adopted algorithms, which can be used to characterize the temperature, pressure and humidity, the contribution will focus on a method for automatic processing these data, based on the use of a distributed architecture. This paper aims at being a possible application of grid computing for scientific research