Enhancing Tropospheric Humidity Data Records from Satellite Microwave and Radiosonde Sensors
Doktorsavhandling, 2015

Water vapor is the most dominant greenhouse gas and plays a critical role in the climate by regulating the Earth's radiation budget and hydrological cycle. A comprehensive dataset is required to describe the temporal and spatial distribution of water vapor, evaluate the performance of climate and weather prediction models in terms of simulating tropospheric humidity, and understand the role of water vapor and its feedback in the climate system. Satellite microwave and radiosonde measurements are two important sources of tropospheric humidity. However, both datasets are subject to errors and uncertainties. The goal of this dissertation was to develop techniques for quantifying and correcting errors in both radiosonde and microwave satellite data. These techniques can be used to homogenize the datasets in order to develop tropospheric humidity climate data records. The quality of operational radiosonde data were investigated for different sensor types. It was found that the use of a variety of sensors over the globe introduces temporal and spatial errors in the data. Further, it was shown that the daytime radiation dry bias, which is one the most important errors in radiosonde data, depends on both sensor type and radiosonde launch time. The error significantly decreases if daytime data are collected near sunrise or sunset. Radiometric errors in satellite data were investigated using both intercomparison of coincident observations as well as validation versus high-quality radiosonde and global positioning system radio occultation data. The results showed that the data from recently launched microwave sounders have a good accuracy relative to each other and simulated data. However, the absolute accuracy of the microwave satellite data can still not be validated due to the lack of reference measurements. In addition, a novel technique for correcting geolocation errors in microwave satellite data was developed based on the difference between ascending and descending observations along the coastlines. Using this method, several important errors including timing errors up to a few hundred milliseconds, and sensor mounting errors up to 1.2 degree were found in some of the microwave instruments. Finally, since satellite data are indirect measurements, a method was developed to transform satellite radiances from different water vapor channels to layer averaged humidity. The technique is very fast because radiative transfer calculations are only required to determine the empirical coefficients.

CDR

climate

microwave

radiosonde

water vapor

remote sensing

antenna

homogenization

humidity

meteorology

troposphere

radio-frequency

sal EA, Hörsalsvägen 11, Chalmers, Göteborg
Opponent: Dr. Roger Saunders, UK Met Office, Exeter, UK

Författare

Isaac Moradi

Chalmers, Rymd- och geovetenskap, Global miljömätteknik och modellering

Vattenånga är den mest dominerande växthusgasen och spelar en avgörande roll i klimatet genom att reglera jordens strålningsbudget och hydrologiska cykeln. En omfattande datamängd krävs för att beskriva den tidsmässiga och rumsliga fördelningen av vattenånga, utvärdera klimat- och väder prognosmodeller i termer av att simulera marknära luftfuktighet, och förstå betydelsen av vattenånga och dess återkoppling i klimatsystemet. Satellit mikrovågsugn och radiosondmätningar är två viktiga källor till marknära luftfuktighet. Men båda dataset är föremål för fel och osäkerheter. Målet med denna avhandling var att utveckla metoder för att kvantifiera och korrigera fel i både radiosond och mikrovågsugn satellitdata. Dessa tekniker kan användas för att homogenisera de datamängder för att utveckla troposfären luftfuktighet klimatdataposter.

Ämneskategorier

Geovetenskap och miljövetenskap

ISBN

978-91-7597-142-1

sal EA, Hörsalsvägen 11, Chalmers, Göteborg

Opponent: Dr. Roger Saunders, UK Met Office, Exeter, UK