Horizontal gradients in the wet path delay derived from four years of microwave radiometer data

Abstract. Initial objectives and design of the Benchmark campaign organized within the European COST Action ES1206 (2013-2017) are described in the paper. This campaign has aimed at supporting the development and validation of advanced GNSS tropospheric products, in particular high-resolution and ultra-fast zenith total delays (ZTD) and tropospheric gradients derived from a dense permanent network. A complex dataset was collected for the 8-week period when several extreme heavy precipitation episodes occurred in central Europe which caused severe river floods in this area. An initial processing of data sets from Global Navigation Satellite System (GNSS) and numerical weather models (NWM) provided independently estimated reference parameters – zenith tropospheric delays and tropospheric horizontal gradients. Their provision gave an overview about the product similarities and complementarities and thus a potential for improving a synergy in their optimal exploitations in future. Reference GNSS and NWM results were inter-compared and visually analysed using animated maps. ZTDs from two reference GNSS solutions compared to global ERA-Interim re-analysis resulted in the accuracy at the 10-millimeter level in terms of RMS (with a negligible overall bias), comparisons to global GFS forecast showed accuracy at the 12-millimeter level with the overall bias of -5 mm and, finally, comparisons to mesoscale ALADIN-CZ forecast resulted in the accuracy at the 8-milllimetre level with a negligible total bias. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and the accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications such as severe weather event monitoring and weather nowcasting. The GNSS products revealed a capability of providing more detailed structures in atmosphere than the state-of-the-art numerical weather models are able to capture. Initial study on contribution of hydrometeors (e.g. cloud water, ice or snow) to GNSS signal delays during severe weather reached up to 17 mm in zenith path delay and suggested to carefully account them within the functional model. The reference products will be further exploited in various specific studies using the Benchmark dataset. It is thus going to play a key role in these highly inter-disciplinary developments towards better mutual benefits from advanced GNSS and meteorological products.

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Sentinel-3 Microwave Radiometers: Instrument Description, Calibration and Geophysical Products Performances

Remote Sensing ◽

10.3390/rs12162590 ◽

2020 ◽

Vol 12 (16) ◽

pp. 2590 ◽

Cited By ~ 1

Author(s):

Marie-Laure Frery ◽

Mathilde Siméon ◽

Christophe Goldstein ◽

Pierre Féménias ◽

Franck Borde ◽

...

Keyword(s):

Microwave Radiometer ◽

Instrument Design ◽

Sea Surface ◽

Double Difference ◽

Path Delay ◽

Vicarious Calibration ◽

Difference Methods ◽

Two Parameters ◽

Microwave Radiometers ◽

Single Instrument

Copernicus Sentinel-3 Surface Topography Mission embarks a two-channel microwave radiometer combined with the altimeter in order to correct the altimeter range for the excess path delay resulting from the presence of water vapour in the troposphere. The in-flight calibration of a single instrument is the critical point to achieve the expected performances. In the context of a constellation, the inter-calibration is even more important. After a presentation of the instrument design, we present the diagnoses used for the calibration of Sentinel-3A, using vicarious calibration over specific areas and double difference methods. The inter-calibration of Sentinel-3B with Sentinel-3A is performed during the tandem phase, using the residual differences of co-located measurements. Finally performances are assessed at crossover points with two parameters, first the wet troposphere correction by comparison with Jason-3; secondly on the Sea Surface Height by difference of variance. Analysis results have shown that Sentinel-3A is well calibrated, consistent with other instruments, and that Sentinel-3B is calibrated within 0.4 K with Sentinel-3A as a reference. Performances and stability fulfill the requirements for both missions.

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Tropospheric wet path-delay measurements

IRE Transactions on Antennas and Propagation ◽

10.1109/tap.1982.1142808 ◽

1982 ◽

Vol 30 (3) ◽

pp. 502-505 ◽

Cited By ~ 14

Author(s):

G. Elgered

Keyword(s):

Path Delay ◽

Wet Path Delay

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Modelling the Altitude Dependence of the Wet Path Delay for Coastal Altimetry Using 3-D Fields from ERA5

Remote Sensing ◽

10.3390/rs11242973 ◽

2019 ◽

Vol 11 (24) ◽

pp. 2973 ◽

Cited By ~ 2

Author(s):

Telmo Vieira ◽

M. Joana Fernandes ◽

Clara Lázaro

Keyword(s):

Geographic Location ◽

Global Navigation Satellite Systems ◽

Path Delay ◽

Satellite Systems ◽

Altitude Dependence ◽

External Sources ◽

Maximum Root ◽

Rms Error ◽

Wet Path Delay ◽

Global Navigation Satellite

Wet path delay (WPD) for satellite altimetry has been provided from external sources, raising the need of converting this value between different altitudes. The only expression available for this purpose considers the same altitude reduction, irrespective of geographic location and time. The focus of this study is the modelling of the WPD altitude dependence, aiming at developing improved expressions. Using ERA5 pressure level fields (2010–2013), WPD vertical profiles were computed globally. At each location and for each vertical profile, an exponential function was fitted using least squares, determining the corresponding decay coefficient. The time evolution of these coefficients reveals regions where they are highly variable, making this modelling more difficult, and regions where an annual signal exists. The output of this modelling consists of a set of so-called University of Porto (UP) coefficients, dependent on geographic location and time. An assessment with ERA5 data (2014) shows that for the location where the Kouba coefficient results in a maximum Root Mean Square (RMS) error of 3.2 cm, using UP coefficients this value is 1.2 cm. Independent comparisons with WPD derived from Global Navigation Satellite Systems and radiosondes show that the use of UP coefficients instead of Kouba’s leads to a decrease in the RMS error larger than 1 cm.

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First Three Years of the Microwave Radiometer aboard Envisat: In-Flight Calibration, Processing, and Validation of the Geophysical Products

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech1878.1 ◽

2006 ◽

Vol 23 (6) ◽

pp. 802-814 ◽

Cited By ~ 33

Author(s):

E. Obligis ◽

L. Eymard ◽

N. Tran ◽

S. Labroue ◽

P. Femenias

Keyword(s):

Microwave Radiometer ◽

Radiative Transfer Model ◽

Altimeter Data ◽

Transfer Model ◽

Path Delay ◽

Inversion Algorithm ◽

Weather Forecasts ◽

Brightness Temperatures ◽

Medium Range ◽

Satellite Altimeter Data

Abstract The Envisat microwave radiometer is designed to correct the satellite altimeter data for the excess path delay resulting from tropospheric humidity. Neural networks have been used to formulate the inversion algorithm to retrieve this quantity from the measured brightness temperatures. The learning database has been built with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and simulated brightness temperatures by a radiative transfer model. The in-flight calibration has been performed in a consistent way by adjusting measurements on simulated brightness temperatures. Finally, coincident radiosonde measurements are used to validate the Envisat wet-tropospheric correction, and this comparison shows the good performances of the method.

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