S. B. Healy

Prospects of the EPS GRAS Mission For Operational Atmospheric Applications

Abstract Global Navigation Satellite System (GNSS) Receiver for Atmospheric Sounding (GRAS) is a radio occultation instrument especially designed and built for operational meteorological missions. GRAS has been developed by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) in the framework of the EUMETSAT Polar System (EPS). The GRAS instrument is already flying on board the first MetOp satellite (MetOp-A) that was launched in October 2006. It will also be on board two other MetOp satellites (MetOp-B and MetOp-C) that will successively cover the total EPS mission lifetime of over 14 yr. GRAS provides daily about 600 globally distributed occultation measurements and the GRAS data products are disseminated to the users in near–real time (NRT) so that they can be assimilated into numerical weather prediction (NWP) systems. All GRAS data and products are permanently archived and made available to the users for climate applications and sc...

Scaling of GNSS Radio Occultation Impact with Observation Number Using an Ensemble of Data Assimilations

AbstractAn ensemble of data assimilations (EDA) approach is used to estimate how the impact of Global Navigation Satellite System (GNSS) radio occultation (RO) measurements scales as a function of observation number in the ECMWF numerical weather prediction system. The EDA provides an estimate of the theoretical analysis and short-range forecast error statistics, based on the ensemble “spread,” which is the standard deviation of the ensemble members about the ensemble mean. This study is based on computing how the ensemble spread of various parameters changes as a function of the number of simulated GNSS RO observations. The impact from 2000 up to 128 000 globally distributed simulated GNSS RO profiles per day is investigated. It is shown that 2000 simulated GNSS RO measurements have an impact similar to real measurements in the EDA and that the EDA-based impact of real data can be related to the impact in observing system experiments. The dependence of the ensemble statistics on observation error statist...

GNSS Radio Occultation Constellation Observing System Experiments

AbstractObserving system experiments within the operational ECMWF data assimilation framework have been performed for summer 2008 when the largest recorded number of Global Navigation Satellite System (GNSS) radio occultation observations from both operational and experimental satellites were available. Constellations with 0%, 5%, 33%, 67%, and 100% data volume were assimilated to quantify the sensitivity of analysis and forecast quality to radio occultation data volume. These observations mostly constrain upper-tropospheric and stratospheric temperatures and correct an apparent model bias that changes sign across the upper-troposphere–lower-stratosphere boundary. This correction effect does not saturate with increasing data volume, even if more data are assimilated than available in today’s analyses. Another important function of radio occultation data, namely, the anchoring of variational radiance bias corrections, is demonstrated in this study. This effect also does not saturate with increasing data vo...

Microwave Absorption, Emission and Scattering: Trace Gases and Meteorological Parameters

Space-borne remote sensing techniques are widely used today to investigate the atmosphere, both by operational and experimental instruments on a large number of satellites. Sensors operating in the microwave range, defined as being wavelengths from 10 to 0.1 cm, frequency 3–300 GHz (microwaves also comprise sub-millimetre waves or frequencies up to 3,000 GHz) of the electromagnetic spectrum were among the first instruments used for this purpose from the ground and on board air- and space-borne platforms. Those instruments measured the thermal emission from a molecular resonance or used the absorption and scattering properties of water droplets or ice crystals to obtain information on atmospheric parameters and composition.

GNSS Transpolar Earth Reflectometry exploriNg System (G-TERN): Mission Concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA’s Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a “dynamic mapper” of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025–2030 or optimally 2025–2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.

Global Atmospheric Data from CHAMP and GRACE-A: Overview and Results

The German geoscience satellite CHAMP (CHAllenging Minisatellite Payload) provides global atmospheric measurements almost continuously since early 2001. It currently generates a unique and operationally available long-term set of GPS radio occultation (RO) data. RO data from the US-German GRACE-A satellite (Gravity Recovery and Climate Experiment) are in addition operationally available since May 22, 2006. Data and analysis results from both satellites are provided to the international scientific community and stimulated several activities to improve GPS RO data analysis and the application in atmospheric research and for global weather forecasts. The data are currently in use by more than 40 research groups worldwide. A near-real time data provision from CHAMP and GRACE was installed and is demonstrated by GFZ within the GEOTECHNOLOGIEN research project NRT-RO (Near-Real-Time Radio Occultation) funded by the German Federal Ministry of Education and Research (BMBF). An average delay between measurement aboard the satellites and provision of corresponding analysis results below 2 h is operationally reached. This successful research activity was one of the preconditions for the beginning of the operational GPS RO data use to improve global weather forecasts in 2006 by Met Office and ECMWF (European Centre for Medium-Range Weather Forecasts). This result is a milestone and a breakthrough for the acceptance of the innovative GPS RO data in Numerical Weather Prediction (NWP).