Springer Atmospheric Sciences Johannes Böhm Harald Schuh Editors Atmospheric Effects in Space Geodesy Springer Atmospheric Sciences For furthervolumes: http://www.springer.com/series/10176 Johannes Böhm Harald Schuh • Editors Atmospheric Effects in Space Geodesy 123 Editors Johannes Böhm HaraldSchuh Department of Geodesy and Department1GeodesyandRemoteSensing Geoinformation Helmholtz Centre Potsdam GFZ German Vienna Universityof Technology Research Centre forGeosciences Vienna Potsdam Austria Germany ISSN 2194-5217 ISSN 2194-5225 (electronic) ISBN 978-3-642-36931-5 ISBN 978-3-642-36932-2 (eBook) DOI 10.1007/978-3-642-36932-2 SpringerHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2013936539 (cid:2)Springer-VerlagBerlinHeidelberg2013 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. 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While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Wir leben auf dem Grunde eines Meeres, des Luftmeeres (Bretterbauer 1969) Foreword Geodesy is the science concerned with the figure of theEarth(geokinematicsand the terrestrial reference frame), the gravity field of the Earth, and Earth rotation; the modern study of these elements requires very precise measurements. Because of this required precision, many components of the Earth must be taken into account.Thattheatmosphereplaysanespeciallyimportantroleingeodesyismost remarkablebecause,ofalltheterrestrialcomponents,itisinfacttheleastmassive. However due to its mobility, its strong dynamic nature, and its interaction with solarradiation,theatmosphere’simportanceiswelloutofproportiontoitsrelative size. I am pleased to introduce some background related to the use of atmospheric informationinspace geodesy,thetopic ofwhich iscoveredherebymyvery able colleaguesattheViennaUniversityofTechnology.Inabroadsense,wecannote the overall concept of Earth system science, in which the links between all the terrestrialcomponentscan beimportant,includingthosebetweenthe atmosphere, solid Earth, ocean, hydrosphere, core, and the external near-space environment. The influence of one component may be noted in the others, and because of this connection,observationsinonedomainareoftenimpactedbythepresenceofthe other. As an atmospheric scientist, my interest in the global scales and these inter- activeconceptswasfirstinspiredbyworkingwithmygraduateadvisors,VictorP. Starr and Edward N. Lorenz, at the Massachusetts Institute of Technology. Prof. Starr had the vision to organize a library of available observations of the global atmosphere and to examine, according to physical principles, its general circula- tion, with an emphasis on the separate angular momentum, hydrological, and energy cycles on a broad scale. Starr surmised, in particular, that changes in the overallangularmomentumoftheatmospherecanexist,andwouldofnecessitybe realizedinchangesinotherterrestrialcomponents,notablyinthesolidEarth.Prof. Lorenz’s research used the overall framework of this diagnostic viewpoint, expanding its theoretical basis, and extending it to view the atmosphere prog- nostically. His models simulated the basic elements of the atmosphere in order to understand the underlying uncertainty in atmospheric forecasts, and by extension that of all chaotic flow. vii viii Foreword The atmospheric influence on the Earth’s rotation was beginning to be con- sidered, and, together with Richard Rosen at Atmospheric and Environmental Research, I became involved with the space geodesy community in this context. Our first connections were through NASA’s LAGEOS and Crustal Dynamics Projects, which, in addition to their study of terrestrial plate motions, produced some of the earlier measurements of Earth rotation and polar motions with high accuracy and temporal resolution. We used independent analyses of the atmo- sphere to calculate series of atmospheric angular momentum, and demonstrated close agreement with the then emerging series of Earth rotation (length of day) values. The geodesy and astronomy communities quickly appreciated the importance of this connection and supported the maintenance of a database for relevant atmospheric statistics. I helped organize, at their request, a special bureau for angular momentum under the organization that has now become the International Earth Rotation and Reference Systems Service. Eventually, the broader signifi- canceoftheatmosphereingeodesyledtotheenhancementofthisSpecialBureau for the Atmosphere’s mission. We now include atmospheric applications, related togravity,loading,andtroposphericpathdelay.Thismissioncouldbeextendedto theevenhigherrealmoftheionosphere,theregioncriticaltothesignalsneededto interpret space-geodetic data. When discussing the need for atmospheric information for geodesy, other aspects of Earth system science emerge, including the interactions between the atmosphere and ocean; an important topic here is how the ocean responds to the overlyingatmosphericpressure.Theroleofthehydrologicalcycleisparamountin geodeticapplicationstoo,includingthesignatureandvariabilityofmoistureinthe atmosphere, which change the massdistributionand influence calculations ofwet path delays. These effects culminate in links with the solid Earth, including also the loading and the effects on the gravity field. The importance of the changing pressurepatterns,sowellknowninweatheranalysisandforecasting,intheselatter applications, was striking to me. The tidal structure of the atmosphere, as is also noted in the book, has prominent importance in geodetic applications. These days we are concerned more than ever about the consequences of potentialclimatechange,whichhavebeenbothobservedandassessedbymodels. Important areas of concern regarding a modified climate are changes in the tem- perature and moisture fields. Add to this the related changes in the circulation systems,andwehaveingredientsthatwillimpactanumberofgeodeticparameters as well. Atmospheric science is a discipline that now uses the numerical weather pre- diction system as one of its major tools. This complex set of procedures is run routinely at the world’s largest weather centers. Such systems include analysis of the atmosphere based on a combination of observations from radiosondes, satel- lites, surface, and other measurements, which are then assimilated according to their locations and error characteristics. The resulting operational fields are pro- jected into the future according to physics and fluid dynamical equations, with short-termforecasts usedintheassimilations.Themeteorologicalcommunityhas Foreword ix also produced so-called reanalysis fields, which have a more consistent set of characteristics over a lengthy period. Geodeticscientistsarenowusingbothoperationalandreanalysisfieldsintheir applications. The fact that this information is of such importance to the geodetic community will be heartening to meteorologists who see the usefulness of their data in another discipline. Indeed, a cross-discipline exchange of information about the atmosphere is of fundamental importance, and will help the overall concepts of Earth system science. The opportunity to make regular visits to the Advanced Geodesy group at the Vienna University of Technology, with Profs. Johannes Böhm and Harald Schuh and their collaborators and students, provided me a chance to enhance the inter- actions with geodetic scientists in a most productive environment, particularly with those who consider the atmosphere of paramount importance in the deter- minationofgeodeticparameters.IthanktheAustrianScienceFundforsupportof these interactions, the US National Science Foundation for research support, the US National Oceanic and Atmospheric Administration for their cooperation in setting up and running the special bureau, and the worldwide community of solid Earth, atmospheric, geodetic, and astronomical scientists, with whom I have interacted, for much inspiration and help. It has been a truly interdisciplinary journey.Manyaspectsofthisinteractivesciencewillbeevidentinthechaptersto follow. Lexington, December 2012 David Salstein Preface DedicatedlecturesonAdvancedGeodesy(HöhereGeodäsie)atViennaUniversity ofTechnology(erstwhilek.k.PolytechnischesInstitut)wereoriginatedin1857by JosefHerr,atthattimeProfessorofAppliedGeometry(PraktischeGeometrie)and later also of Advanced Geodesy and Spherical Astronomy (Höhere Geodäsie und Sphärische Astronomie). Since those early days of Advanced Geodesy in Vienna, research topics have been manifold and broad, being revolutionized with the adventofcomputersandsatellitesinthesecondhalfofthetwentiethcentury.This development certainly strengthened the value of studies dealing with atmospheric effectsingeodesy.Forinstance,in1969KurtBretterbauer,predecessorofHarald SchuhasChairofAdvancedGeodesy,wrotehisdissertationonrefractionissuesin Advanced Geodesy, stating in the first sentence of the introduction to the thesis that we are living at the bottom of a sea, the’air-sea’ (Wir leben auf dem Grunde eines Meeres, des Luftmeeres). The substance of this quote should not be under- rated, as many atmospheric effects have counterparts in the oceans, e.g., atmo- spheric and oceanic loading of the solid Earth, excitation of Earth rotation, or variable gravitational effects due to density variations in both fluids. While there are no antennas at the ocean bottom to receive signals from satellites or extra- galactic radio sources, systems with receivers and transponders at the sea surface exist as well as sensors located at the bathymetry. Ever since Johannes Böhm completed his Ph.D. thesis on tropospheric path delays of Very Long Baseline Interferometry (VLBI) observations in 2004 supervised by Harald Schuh, the research group on Advanced Geodesy at Vienna UniversityofTechnologyhasbeenveryactiveininvestigatingatmosphericeffects in space geodesy. Johannes Böhm’s thesis laid the foundation for the Vienna Mapping Functions 1 (VMF1) and the Global Mapping Functions (GMF), which were published in 2006 and can be used to map tropospheric delays from the zenith to arbitrary elevations. In the wake of this work, numerous research and Ph.D. projects were stimulated by issues relating to tropospheric delays, e.g., the determination of long-term trends in zenith delays determined from VLBI observations (Ph.D. thesis by Robert Heinkelmann, finished in 2008) or the retrievalofprecipitablewaterwithGlobalNavigationSatelliteSystems(GNSS)— a topic that has been primarily dealt with in projects led by Robert Weber with Ph.D. theses, e.g., by Elisabeth Klaffenböck in 2005 or Ana Karabatic in 2011. xi xii Preface Under the supervision of Harald Schuh, Thomas Hobiger completed his Ph.D. thesis on the determination of ionospheric parameters from VLBI observations in 2005.Hisstudymarksthestartingpointofresearchonionosphericeffectsinspace geodesy,andwascontinuedbySonyaTodorova(Ph.D.in2008),MahdiAlizadeh, Nina Magnet, and Claudia Tierno Ros. Adiversificationofresearchtopicsbeyondthefieldofatmosphericdelaysarose when the Austrian Science Fund (FWF, Der Wissenschaftsfond) approved project GGOS Atmosphere in October 2008. GGOS is the Global Geodetic Observing SystemoftheInternationalAssociationofGeodesy(IAG),aimedattheconsistent treatment of geokinematics (i.e., the shape of the Earth), the gravity field of the Earth, and Earth rotation. In accordance with those pillars, GGOS Atmosphere allowed funding of three scientists dealing with atmospheric loading (Dudy Wi- jaya), atmospheric effects on gravity (Maria Karbon), and atmospheric excitation of Earth rotation (Michael Schindelegger). Additionally, Vahab Nafisi and Matthias Madzak addressed the refinement of ray-tracing through numerical weathermodels.AllscientistsinprojectGGOSAtmosphereconsistentlyuseddata from numerical weather models of the European Centre for Medium-Range Weather Forecasts (ECMWF) for the determination of the respective products. Since 2002, Johannes Böhm has been giving these lectures on Atmospheric effectsinspacegeodesyattheViennaUniversityofTechnology.Supportedbythe input of the research staff of Advanced Geodesy, these lectures present both theoretical foundations as well as recent results achieved in the field. Conse- quently, with all the expertise available, we decided to write a book based on the contributions of various members of the research group. Instead of simply com- piling numerous papers, the plan was to publish a textbook with a consistent and homogeneous description of atmospheric effects that can be used for lectures, primarily in geodesy courses. The first chapter (Geodetic and Atmospheric Background) by Böhm et al. provides introductory information for the other chapters in the textbook, sum- marizing gas laws and meteorological parameters or phenomena for the tropo- sphere, as well as ionization processes for the ionosphere. More specifically, the second chapter (Ionospheric Effects on Microwave Signals) by Alizadeh et al. discussesdelays(andphaseadvances)ofsignalsfromspacegeodetictechniquesin the ionosphere, and how they are treated in the analysis of the observations. Analogously, in the third chapter (Path Delays in the Neutral Atmosphere), Nilsson et al. report about signal delays in the neutral atmosphere. In both cases, ionosphere and neutral atmosphere, the emphasis of the book is on atmospheric effectsonspacegeodeticobservationsandhowtheycanbereducedormitigatedto get the best possible geodetic results in terms of station coordinates or Earth orientation parameters. However, the contributions do not deal with the reverse applications,thatistheuseofspacegeodeticobservationsforthedeterminationof atmospheric parameters in the first place, e.g., maps of water vapor or Total Electron Content. ‘‘Atmospheric Pressure Loading’’ by Wijaya et al. describes atmospheric loading of the solid Earth by changing surface pressure and its implication on geometric space geodetic techniques, while in the fifth chapter