In a climate change era, measuring atmospheric parameters is fundamental for monitoring the status and predicting the patterns of the atmosphere. For this reason, several space missions, already launched or to be launched by different space agencies are devoted to these measurements. While most key parameters are or will be available, some others are still missing. Among them, the water vapor (WV) in the bottom part of the troposphere, which can contribute to improve numerical weather prediction models (NWP) on short time scales. In order to fill these gaps, a method for obtaining the integrated water vapor (IWV) along a microwave link and based on a pair of attenuation measurements, called NDSA (Normalized Differential Spectral Attenuation), was proposed years ago. The NDSA method is based on measuring a parameter called "spectral sensitivity", which is the normalized incremental ratio of the spectral attenuation and was found to be linearly related to the IWV along the radio-link path. Some studies, supported by ESA, have shown the NDSA capability to effectively estimate the IWV along the path between two Low Earth Orbit (LEO) satellites - one carrying a transmitter, the other a receiver - in a limb measurement geometry, using transmission frequencies in the Ku and K bands for paths crossing the low troposphere (below 10 km), or much higher in case higher tropospheric layers are involved. The ESA studies focused on the retrieval of vertical profiles of IWV and WV in the case of LEO satellites orbiting in the same plane, but along opposite directions (counter-rotating), and only marginally the very different case of the application of the NDSA technique to satellites orbiting in the same plane and along the same direction (co-rotating). The latter is the concept of a recent project, SATCROSS, supported by the Italian Space Agency: the objective is providing a pre-feasibility study for a space remote sensing system based on a train of co-rotating LEO satellites. In such a configuration, in which one or more LEO satellites with an on-board transmitter follow(s) one or more LEO satellites with receiving apparatuses, the NDSA measurements refer to links that cross the troposphere at certain altitudes and "brush" an entire annular region in the orbital plane. It is thus possible to estimate the two-dimensional field of WV in the aforementioned annular region starting from the entire set of IWV measurements based on an inverse problem formulation. Specific SATCROSS activities are: 1) analysis and application of appropriate two-dimensional inversion algorithms; 2) development of an end-to-end simulator; 3) analysis of the impact of the WV products on NWP; 4) definition of the mission characteristics and of the satellites payload, based on Cubesat technology. As a support to these activities, a measurement campaign is being carried out in a ground-to-ground configuration with an instrument able to provide NDSA measurements at 19 GHz. The purpose of this presentation is to illustrate the overall framework of the SATCROSS project, while the details of the related activities are given by companion presentations in ATMOS 2021.
Tropospheric water vapor observation from space through a new measurement concept: the SATCROSS Project
UGO CORTESI;GIOVANNI MACELLONI;MARCO GAI;SAMUELE DEL BIANCO;FRANCESCO MONTOMOLI;ALBERTO ORTOLANI;SAMANTHA MELANI;LUCA ROVAI;
2021
Abstract
In a climate change era, measuring atmospheric parameters is fundamental for monitoring the status and predicting the patterns of the atmosphere. For this reason, several space missions, already launched or to be launched by different space agencies are devoted to these measurements. While most key parameters are or will be available, some others are still missing. Among them, the water vapor (WV) in the bottom part of the troposphere, which can contribute to improve numerical weather prediction models (NWP) on short time scales. In order to fill these gaps, a method for obtaining the integrated water vapor (IWV) along a microwave link and based on a pair of attenuation measurements, called NDSA (Normalized Differential Spectral Attenuation), was proposed years ago. The NDSA method is based on measuring a parameter called "spectral sensitivity", which is the normalized incremental ratio of the spectral attenuation and was found to be linearly related to the IWV along the radio-link path. Some studies, supported by ESA, have shown the NDSA capability to effectively estimate the IWV along the path between two Low Earth Orbit (LEO) satellites - one carrying a transmitter, the other a receiver - in a limb measurement geometry, using transmission frequencies in the Ku and K bands for paths crossing the low troposphere (below 10 km), or much higher in case higher tropospheric layers are involved. The ESA studies focused on the retrieval of vertical profiles of IWV and WV in the case of LEO satellites orbiting in the same plane, but along opposite directions (counter-rotating), and only marginally the very different case of the application of the NDSA technique to satellites orbiting in the same plane and along the same direction (co-rotating). The latter is the concept of a recent project, SATCROSS, supported by the Italian Space Agency: the objective is providing a pre-feasibility study for a space remote sensing system based on a train of co-rotating LEO satellites. In such a configuration, in which one or more LEO satellites with an on-board transmitter follow(s) one or more LEO satellites with receiving apparatuses, the NDSA measurements refer to links that cross the troposphere at certain altitudes and "brush" an entire annular region in the orbital plane. It is thus possible to estimate the two-dimensional field of WV in the aforementioned annular region starting from the entire set of IWV measurements based on an inverse problem formulation. Specific SATCROSS activities are: 1) analysis and application of appropriate two-dimensional inversion algorithms; 2) development of an end-to-end simulator; 3) analysis of the impact of the WV products on NWP; 4) definition of the mission characteristics and of the satellites payload, based on Cubesat technology. As a support to these activities, a measurement campaign is being carried out in a ground-to-ground configuration with an instrument able to provide NDSA measurements at 19 GHz. The purpose of this presentation is to illustrate the overall framework of the SATCROSS project, while the details of the related activities are given by companion presentations in ATMOS 2021.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
