Skip to main content

ESA Data Ontology

Search from vocabulary

Content language

Concept information

... > Instruments > Earth Remote Sensing Instruments > Passive Remote Sensing > Positioning/Navigation > GPS > GRAS

Preferred term

GRAS  

Definition

  • GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) is a new European GNSS (Global Navigation Satellite System) receiver that operates as an atmospheric sounder. It will provide unprecedented observations of atmospheric temperature and humidity to improve weather forecasting and climate change monitoring. GRAS uses radio occultation to measure vertical profiles of atmospheric temperature and humidity by tracking signals received from a constellation of GPS navigation satellites while they are setting or rising behind the Earth's atmosphere. Radio occultation is based on the fact that when radio waves pass through the atmosphere, either during a rise event or during a set event as seen by the receiver, they are refracted along the atmospheric path. The degree of refraction depends on gradients of air density, which in turn depend on temperature and water vapour. Therefore, measurement of the refracted angle contains information about these atmospheric variables. As the measurements are made tangentially to the atmosphere, the profiles will be provided with a resolution within a few hundred metres to 1.5 kilometres, while horizontal coverage of each profile is in the order of a few hundred kilometres. The GRAS instrument will provide 500 very precise atmospheric profiles per day, which will be fed into Numerical Weather Prediction (NWP) models to improve the accuracy of weather forecasts. At the same time, due to the very good stability of the instrument, GRAS measurements will contribute to monitoring climate change. GRAS can track up to eight satellites for navigation purposes, two additional satellites for rise and two others for set occultation measurements. GRAS has on-board GPS satellite prediction for optimising the navigation and occultation measurements. Source: ESA Group: Instrument_Details Entry_ID: GRAS Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Passive Remote Sensing Instrument_Type: Positioning/Navigation Instrument_Subtype: GPS Short_Name: GRAS Long_Name: Global navigation satellite system Receiver for Atmospheric Sounding End_Group Group: Instrument_Associated_Sensors Short_Name: GPS SONDE Short_Name: GRAS Short_Name: GPS RECEIVERS End_Group Group: Associated_Platforms Short_Name: METOP Short_Name: METOP-A Short_Name: METOP-B End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: Radio Number_Channels: 8 End_Group Online_Resource: http://oiswww.eumetsat.org/WEBOPS/eps-pg/GRAS/GRAS-PG-0TOC.htm Creation_Date: 2007-09-13 Group: Instrument_Logistics Data_Rate: 60 kb/s Instrument_Owner: ESA/Eumetsat End_Group End_Group (en)

Broader concept

Change note

  • 2019-02-22 13:22:50.0 [mmorahan] insert WeightedRelation (id: null related concept uuid: 6120cea0-c943-4c7c-bddd-8d8648d58022 relationship type: null relationship value: null generated by: null);

URI

https://gcmd.earthdata.nasa.gov/kms/concept/69f341d1-e29f-4bb9-b3b7-27ce4533f2ad

Download this concept:

RDF/XML TURTLE JSON-LD Last modified 12/6/20