Manila Observatory explores possibility of 3D water vapor monitoring via GPS technology

by Quirino Sugon Jr.

Dr. Rui Fernandes, Dr. Nofel Lagrosas, and Dr. Durairaju Raju at the Manila Observatory's Klima Conference Room

Dr. Rui Fernandes, Dr. Nofel Lagrosas, and Dr. Durairaju Raju at the Manila Observatory's Klima Conference Room

Last 8 July 2011, scientists from Manila Observatory met with their counterparts in Singapore and Portugal.  From  Manila Observatory are Mr. James Simpas (Instrumentation Technology Division/Urban Air Quality), Dr. Quirino Sugon Jr. (Iono-Geomagnetics Studies), and Dr. Nofel Lagrosas(Urban Air Quality and Chair of the Ateneo Physics Department).  The visitors are  Dr. Rui Fernandes of University of Beira Interior, Portugal and  Dr Durairaju Kumaran Raju of the Tropical Marine Science Institute, National University of Singapore.  The purpose of the meeting is to explore ways on how to collaborate in using GPS (Global Positioning System) for research.  Manila Observatory has several GPS stations installed by Jet Propulsion Laboratory (JPL) and the Scintillation Detection Aid (SCINDA) network.

A GPS is a constellation of 24 satellites orbiting the earth that allows precise determination of position of a receiver using at least the orbital information of 4 satellites. GPS satellites have atomic clocks which are corrected using the principles of Einstein’s General Relativity, because clocks aboard flying planes appear to tick faster than clocks on the ground–a phenomenon called gravitational time dilation.  The GPS was conceived during the Cold War when American scientists, using the aid of powerful computers, were able to deduce the position of the Russian Sputnik satellite using the principle of Doppler effect: an observer receives signals from an object at higher frequency when the object is moving towards the observer and at lower frequency when the object is moving away–just like the sound of speeding car as it whizzes past you.  In the GPS, we are faced with an inverse problem: if we accurately know the position of the satellites, can we know our location on earth?

Dr. Fernandes made a pen-and-whiteboard presentation on how to use GPS for measuring water vapor.  Similar studies were done before at the Manila Observatory by Faye Cruz and Fr. Jett Villarin (Science Diliman 2000) and R. Reyes and Fr. Daniel McNamara (Manila Observatory Report 2000).  But these studies were only for making a normalized measurement of water vapor column along the zenith, i.e., straight up.  What Dr. Fernandes proposed is to use a network of GPS stations to make a time-varying 3D map of water vapor across an area such as Manila.  This water vapor measurements can then be fed into climate change models, such as those run by Dr. Gemma Narisma of the Regional Climate Systems of Manila Observatory, in order to make better predictions of climate variability.

The path of GPS signals is delayed by the ionosphere and the local weather, in the same way as light bends in water or how mirages form in the desert.  To remove the effects of the ionosphere delay, two signal frequencies were used and these are fed into certain equations.  To remove the effects of the dry air delay, the weather is modeled and its temperature and pressure parameters are determined from meteorological data.  So the remaining delay in GPS is solely due to precipitable water vapor (PWV)–the water vapor that may condense to form rain. Using an array of GPS stations, the water vapor column between receivers and the satellites can be measured and the 3D picture of water vapor can be obtained and how this evolve in time.

Last 29 July 2011, the Manila Observatory, in the name of Fr. Daniel J. McNamara, SJ, submitted a summary proposal to Asia Pacific Network for funding.  The collaborators in the proposed project are the scientists at Manila Observatory together with Dr. Rui Fernandes, Dr. Durairaju Raju, and Dr Nitin Tripathi of the Asian Institute of Technology, Thailand (who was not able to come).  We hope that the project pushes through.

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About ateneophysicsnews
Physics News and Features from Ateneo de Manila University

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