On the accuracy of integrated water vapor observations and the potential for mitigating electromagnetic path delay error in InSAR

Abstract. A field campaign was carried out in the framework of the Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects (METAWAVE) project sponsored by the European Space Agency (ESA) to investigate the accuracy of currently available sources of atmospheric columnar integrated water vapor measurements. The METAWAVE campaign took place in Rome, Italy, for the 2-week period from 19 September to 4 October 2008. The collected dataset includes observations from ground-based microwave radiometers and Global Positioning System (GPS) receivers, from meteorological numerical model analysis and predictions, from balloon-borne in-situ radiosoundings, as well as from spaceborne infrared radiometers. These different sources of integrated water vapor (IWV) observations have been analyzed and compared to quantify the accuracy and investigate the potential for mitigating IWV-related electromagnetic path delay errors in Interferometric Synthetic Aperture Radar (InSAR) imaging. The results, which include a triple collocation analysis accounting for errors inherently present in every IWV measurements, are valid not only to InSAR but also to any other application involving water vapor sensing. The present analysis concludes that the requirements for mitigating the effects of turbulent water vapor component into InSAR are significantly higher than the accuracy of the instruments analyzed here. Nonetheless, information on the IWV vertical stratification from satellite observations, numerical models, and GPS receivers may provide valuable aid to suppress the long spatial wavelength (>20 km) component of the atmospheric delay, and thus significantly improve the performances of InSAR phase unwrapping techniques

Tropospheric Products from High-Level GNSS Processing in Latin America

ARTÍCULO PUBLICADO EN REVISTA EXTERNA. The present geodetic reference frame in Latin America and the Caribbean is given by a network of about 400 continuously operating GNSS stations. These stations are routinely processed by ten Analysis Centres following the guidelines and standards set up by the International Earth Rotation and Reference Systems Service (IERS) and International GNSS Service (IGS). The Analysis Centres estimate daily and weekly station positions and station zenith tropospheric path delays (ZTD) with an hourly sampling rate. This contribution presents some attempts aiming at combining the individual ZTD estimations to generate consistent troposphere solutions over the entire region and to provide reliable time series of troposphere parameters, to be used as a reference. The study covers ZTD and IWV series for a time-span of 5 years (2014–2018). In addition to the combination of the individual solutions, some advances based on the precise point positioning technique using BNC software (BKG NTRIP Client) and Bernese GNSS Software V.5.2 are presented. Results are validated using the IGS ZTD products and radiosonde IWV data. The agreement was evaluated in terms of mean bias and rms of the ZTD differences w.r.t IGS products (mean bias 1.5 mm and mean rms 6.8 mm) and w.r.t ZTD from radiosonde data (mean bias 2 mm and mean rms 7.5 mm). IWV differences w.r.t radiosonde IWV data (mean bias 0.41 kg/m2 and mean rms 3.5 kg/m2).Sitio de la revista: https://link.springer.com/chapter/10.1007/1345_2020_12

The usefulness of the Global Navigation Satellite Systems (GNSS) in the analysis of precipitation events

It is well known that the use of the Global Navigation Satellite Systems (GNSS), both with ground-based and Low Earth Orbit (LEO) receivers, allows retrieving atmospheric parameters in all the weather conditions.Ground-based GNSS technique provides the integrated precipitable water vapour (IPWV) with temporal continuity at a specific receiver station, while the GNSS LEO technique allows for Radio Occultation (RO) observations of the atmosphere, providing a detailed atmospheric profiling but without temporal continuity at a specific site.In this work, several precipitation events that occurred in Italy were analysed exploiting the potential of the two GNSS techniques (i.e. ground-based and space-based GNSS receivers). From ground-based receivers, time series of IPWV were produced at specific locations with the purpose of analysing the water vapour behaviour during precipitation events. From LEO receivers, the profiling potential was exploited to retrieve the cloud top altitude of convective events, taking into account that although GNSS RO could capture the dynamics of the atmosphere with high vertical resolution, the temporal resolution is not enough to continuously monitor such an event in a local area. Therefore, the GNSS technique can be considered as a supplemental meteorological system useful in studying precipitation events, but with very different spatial and temporal features depending on the receiver positioning

Satellite air temperature estimation for monitoring the canopy layer heat island of Milan

In this work, satellite maps of the urban heat island of Milan are produced using satellite-based infrared sensor dataFor this aim, we developed suitable algorithms employing satellite brightness temperatures for the direct air temperature estimation 2 m above the surface (canopy layer), showing accuracies below 2KThe air temperatures measured by ground-based weather stations were properly matched with brightness temperatures observed by the Moderate-resolution Imaging Spectroradiometer (MODIS) on board of both Terra and Aqua satellitesIn total, 931 daytime and nighttime scenes taken between 2007 and 2010 were processedAnalysis of the canopy layer heat island (CLHI) maps during summer months reveals an average heat island effect of 3-4K during nighttime (with some peaks around 5K) and a weak CLHI intensity during daytimeIn addition, the satellite maps reveal a well defined island shape across the city center from June to September confirming that, in Milan, urban heating is not an occasional phenomenonFurthermore, this study shows the utility of space missions to monitor the metropolis heat islands if they are able to provide nighttime observations when CLHI peaks are generally significant. © 2012 Elsevier Inc

Comparison between surface and canopy layer urban heat island using MODIS data

Urban heat island (UHI) maps were produced over the city of Milan, Italy, using data provided by the Moderate-resolution Imaging Spectroradiometer (MODIS). Two types of UHI were analyzed simultaneously: the canopy layer heat island (CLHI) and the surface urban heat island (SUHI). The SUHI and CLHI maps allow to monitor the spatial and temporal evolution of surface and air heating and also to highlight the different features (e.g. magnitude, spatial extent, orientation and UHI centre location) using a Gaussian surface fitting. This results indicate that the SUHI effect is a noticeable phenomenon throughout the whole diurnal cycle: it has a stronger intensity in the daytime with peaks around 9-10 K while in the nighttime it decreases by a factor of 2. In contrast, the CLHI during the daytime is absent and after sunset shows features similar to the nighttime SUHI. Although the 1-km spatial resolution of MODIS may represent a limitation for a finer scale analysis, the four daily passes are essential to monitor the urban heat island at different times during the day

Radio occultation and ground-based GNSS products for observing, understanding and predicting extreme events: A review

In this paper we review the contributions of GNSS ground-based and radio occultation receivers to the understanding and prediction of severe weather phenomena around the world. These ground- and space-based GNSS observations, which are complementary to other in-situ and remotely sensed observations, are sensitive to the temperature and water vapor content of the atmosphere, both important parameters that characterize the structure and evolution of heavy rainfall and convective storms, atmospheric rivers, tropical cyclones, and droughts and heat waves. With the first ground-based GPS observations reported in the early 1990s and the first radio occultation observations of Earth's atmosphere derived from the GPS/MET proof-of-concept mission (1995\u20131997), these GNSS-based observations are still relatively new contributors to the research and operational suite of technologies

Monitoring of atmospheric water around precipitation events using a scanning ground-based microwave radiometer

This work considers the use of a dual-frequency, ground-based microwave radiometer with scanning capabilities to investigate the behaviour of the atmosphere in terms of precipitable water vapour and integrated cloud liquid before precipitation events