Exploring the Atmosphere by Remote Sensing Techniques

In recent years, it has emerged that human activities contribute to the c- mate changes of our planet. For this reason, it is essential to understand the chemical and physical processes governing atmospheric balance, to - terminetheconcentrationofatmosphericconstituentsandmonitortheird- tribution worldwide. In situ measurements from ground-based instruments can give detailed local information, but only passive remote sensing inst- ments mounted aboard satellites can generate the global records needed for long-term monitoring of the atmosphere. For these reasons, two schools on remote sensing have been held at the International Centre for Theoretical Physics ICTP at Trieste (founded by the Nobel Prizewinner Abdus Salam) overthelastfouryears. The?rstschool"ExploringtheAtmosphereby- moteSensing"wasmainlydevotedtoatmosphericapplications,whereasthe second"InverseMethodsinAtmosphericSciences"focusedontechniquesto retrieve atmospheric components, gases, aerosol and clouds. More than 140 studentsfromdi?erentcountriesattendedthecoursesand30lecturersint- ducedtheEarthObservationmissionsandthemostadvancedtechniquesto retrieve atmospheric components. This book contains the topics underlying eachofthetwoschools. The?rstcontributionbyPaulSimonandPolymniaSkarlasintroducethe networks,combiningmeasurementsfromvariousinstruments,formingan- tegral part of a general strategy, namely the Integrated Global Observing Strategy(IGOS),whichseekstobringtogetherthemajorground-basedand satellitecomponentsoftheEarth'sobservingsystemforabettere?ectiveness intheiruseandinthestudyoftheenvironment. Thisgivesafewexamples of networks focusing on generating data of known and high quality, to s- port research related to the Earth's atmospheric environment on the sho- andlong-termscales,butalsoassessmentsonglobalchangeandguidancein internationalpolicymaking. A second contribution by Martine DeMaziere covers the exploitation of thesynergybetweengroundandspacemeasurements. Thiscontribution- troduces some remote sensing ground-based observation methods and hi- lightssomeaspectsofatmosphericchanges. Manyreferencesareincludedfor furtherreading. VI Preface AthirdcontributionbyKnutStamnesreviewsforwardmodellingcapab- itiesandrequirementsinconnectionwithremotesensingoftheenvironment. Emphasis is placed on the formulation of the problem and on discussion of recent developments. The plane-parallel radiative transfer model is used as aspeci?cexampleofaforwardmodelthatissimplebutveryuseful. Aso- tiontothisforwardmodelisoutlinedusingthediscreteordinatemethod. A linearizedversionofthisdiscreteordinatesolutionyieldinganalyticweig- ing functions or Jacobians in addition to radiances is also brie?y discussed. This provides a framework for a discussion of computational resource and accuracyrequirements.