SATELLITE OCEANOGRAPHY

Transcription

1 SATELLITE OCEANOGRAPHY An Introduction for Oceanographers and Remote-sensing Scientists I. S. Robinson Lecturer in Physical Oceanography Department of Oceanography University of Southampton JOHN WILEY & SONS Chichester New York Brisbane Toronto Singapore Published in association with PRAXIS PUBLISHING Chichester

2 Table of Contents Foreword 11 Preface 13 Chapter 1 Oceanography from space? 1.1 A new field of marine science? A quarter of a century of ocean observation from space The value of satellite data to oceanography The scope of the book 22 Section A FUNDAMENTALS OF REMOTE SENSING IN OCEANOGRAPHY Chapter 2 The possibilities in space space hardware and data transmission 2.1 Space platforms and their orbits Satellite vehicles Satellite orbital dynamics Spatial and temporal sampling characteristics of orbits Sensors on satellites Sensors in relation to the electromagnetic spectrum Sensor measurements Spatial sampling capabilities of sensors Recent and planned satellite sensors which have oceanographic applications Data retrieval Satellite-to-earth data transmission Data dissemination 56 Chapter 3 The possibilities for oceanography 3.1 The oceanographic capabilities of satellite sensors Ocean science in the 1980s.* Dynamical oceanographic processes Ocean circulation Tides 71

3 6 Table of Contents Fronts Upwelling Mixed-layer dynamics Coastal and estuarine dynamical and topographic phenomena Ocean waves Space and time scales of oceanographic phenomena, in relation to satellite sampling 84 Chapter 4 Principles of remote sensing of the sea 4.1 Introduction Sensor calibration Atmospheric correction Positional registration Geophysical calibration Oceanographic sampling for'sea truth' 100 Chapter 5 Principles of image processing 5.1 Image processing and oceanography Digital image data from satellites Image-processing hardware Geometric processing Masks and overlays Smoothing, filtering, and noise reduction Measurement of spatial variability Enhancement of single-band radiometric information Presentation of multichannel image data Atmospheric correction and geophysical calibration 130 Section В OCEANOGRAPHIC APPLICA TIONS OF SA TELLITE REMOTE SENSING Chapter 6 Visible wavelength 'ocean-colour' sensors 6.1 Introduction Scope Colour sensors on Landsat The Coastal Zone Colour Scanner on Nimbus Aspects of optical theory relevant to ocean-colour viewing from space Definition of some optical quantities Measurements made by a satellite sensor Optical pathways in the atmosphere Practical strategies for the atmospheric correction of visible wavelength data Scattering and absorption of light in sea-water Oceanographic interpretation of ocean colour Light-scattering at the sea surface 164

4 Table of Contents Calibration and application of CZCS data Sensor calibration Atmospheric corrections CZCS calibration algorithms Applications in biological oceanography Applications in dynamical oceanography Oceanographic uses of Landsat MSS data Data processing Calibration of Landsat data for sediment and chlorophyll Sediment movement studied with Landsat data Other oceanographic processes viewed by Landsat Bathymetry using Landsat Coastal geomorphology Oceanographic use of other visible-wavelength satellite data 192 Chapter 7 Sea-surface temperature from infrared scanning radiometers 7.1 Introduction The physics of infrared radiation Thermal emission Atmospheric absorption Infrared sensors Brightness temperature calibration of AVHRR data The near-surface thermal structure in the ocean The skin temperature The thermocline structure of the ocean The sea-surface skin-temperature deviation Surface slicks Atmospheric correction and SST calibration techniques Atmospheric correction strategies Multispectral and multilook techniques Cloud-removal techniques SST operational products The potential uses of SST data from satellites Climatology Global changes in SST Atmospheric response to SST anomalies Weather prediction (1 to 10 days) Gas exchange across the air sea interface Surface heat flux as it affects the ocean heat budget Deep convection and water-mass formation Dynamical oceanography Pollution studies Examples of the application of satellite SST data Global SST, and SST-anomaly, maps Ocean eddies 233

5 8 Table of Contents Upwelling Ocean fronts The Mediterranean Sea Shallow-sea fronts Coastal-fringe fronts Commerical fisheries 246 Chapter 8 Passive microwave radiometers 8.1 The physical principles of passive microwave radiometry Overview Thermal emission in the microwave The radiation received by the satellite antenna Atmospheric and solar radiation effects Sea-surface emissivity Skin depth of sea-surface emission Microwave radiometer design Radiometer design constraints The Seasat and Nimbus 7 SMMR Other satellite microwave radiometers Oceanographic interpretation of passive microwave data from space Potential applications SST and surface-wind retrieval algorithms for SMMR Comparison between infrared and microwave radiometers for SST measurement Applications of SMMR data 272 Chapter 9 Satellite altimetry of sea-surface topography 9.1 Introduction An exciting new oceanographic instrument Principles of satellite altimetry Distance measurement with a radar altimeter The instrument design Corrections for atmospheric transmission Surface roughness errors Altimeter specifications Establishing a datum Orbit determination Summary of height errors relative to the reference ellipsoid The geoid Application of altimetry to the study of ocean currents Geostrophic balance The possibilites for ocean-circulation determination Examples of ocean-circulation phenomena observed with Seasat altimeter data 293

6 Table of Contents Tidal observations with the altimeter The value of satellite altimetry to tidal studies Extraction of tidal information from altimeter data Examples of altimeter applications to ocean-tidal science Ocean bathymetry from satellite altimeters The selection of satellite orbits for altimeters 306 Chapter 10 Active microwave sensing of sea-surface roughness 10.1 Introduction to the remote sensing of sea-surface roughness Radar reflection from the sea surface Backscatter cross-section Specular reflection and scattering Resonant Bragg scattering Polarisation Wind-generated surface-wave roughness Surface films and slicks Dynamical causes of sea-surface roughness patterns Artificial causes of sea-surface roughness patterns 321 Chapter 11 The altimeter as a surface-roughness sensor 11.1 A nadir-viewing radar Physical principles of operation The effect of waves on the return-pulse shape The effect of surface roughness on the return-pulse strength Performance of wave-height algorithms Performance of wind-speed algorithms Oceanographic applications of satellite-altimeter-derived wave height 332 Chapter 12 Synthetic aperture radar 12.1 High-resolution imaging radars Principles of SAR operation SAR geometry Range resolution Azimuth resolution using the synthetic aperture principle SAR processing SAR image errors due to moving targets Image degradation due to speckle SAR imaging of ocean waves A controversial problem Hydrodynamic modulation Electromagnetic modulation Motion effects 368

7 10 Table of Contents High sea states Directional wave spectra from SAR images Observations of ocean waves with Seasat SAR A description of the Seasat SAR Wave imagery Wave spectra from the Seasat SAR Internal waves imaged by SAR Observations of internal waves in Seasat data Internal-wave theory Surface-roughness imaging of internal waves Oceanographic information content of SAR images of internal waves Other oceanographic phenomena imaged by SAR 392 Chapter 13 Microwave scatterometers 13.1 Introduction Wind scatterometry Surface-wind stress and the near-surface wind-velocity profile The development of wind-speed and wind-stress algorithms for interpreting radar backscatter measurements Experience with the Seasat scatterometer The SASS design and operation SASS data processing The SASS wind-vector algorithm Removing the direction alias Validation of the SASS algorithms Applications of wind scatterometry Wave scatterometry 417 Chapter 14 The way forward 14.1 Satellite sensors for oceanography in the future Introduction The ERS-1 payload TOPEX Developments in data analysis Trends in ocean science Conclusion 426 References 428 Index 444