Introduction For more than four decades, satellites have been observing the ocean from several hundred kilometers above the surface of the Earth. From the vantage of space, they have given us a global view of the ocean surface and the atmosphere and their variability. Satellite instruments that are in orbit today detect a broad range of ocean variables that touch on all aspects of oceanography These include sea surface temperature, surface wind velocity, chlorophyll, sea surface elevation, and ice cover, among others. The unifying element of satellite remote sensing is not just that measurements are made from space, but more specifically that satellite instruments detect electromagnetic radiation that is either emitted from or reflected off the surface of the ocean. The main attention will be given to passive and active microwave remote sensing of the ocean-atmosphere system. Lecture consists of two parts: Fundamentals of microwave remote sensing and Applications of satellite microwave data to study the ocean-atmosphere system 1 Outlines I. Fundamentals Introduction to microwave radiometry and radar sensing. The electromagnetic spectrum. Brief history. Application of microwave remote sensing data. Microwave radiometry. Dielectric properties of natural media. Depth of penetration. Emissivity. Brightness temperature. Radiative transfer in the atmosphere-underlying surface system. Radar sensing. Backscattering. Altimeters. Scatterometers. Real Aperture and Synthetic Aperture Radars. Outlines • Microwave antennas and receivers. Directivity, sidelobes and loss. Sensitivity and calibration. Antenna temperature. • Multichannel scanning microwave radiometers: SSM/I, TMI, AMSU, AMSR-E. Surface Moisture and Ocean Salinity (SMOS) and Aquarius missions. Meteor-M N1 MTVZA, GCOM-W1 AMSR2. • Radars: QuikSCAT and ASCAT. ERS-1/2 SAR, Envisat ASAR. RADARSAT -1/2, ALOS PALSAR. • Passive microwave remote sensing. Absorption by atmospheric gases, clouds and precipitation. Sea surface temperature, salinity and wind speed. Sea ice concentration and age. Total atmospheric water vapor content and total cloud liquid water content. Retrieval algorithms for geophysical parameters. • Active microwave remote sensing. Sea-surface wind speed. Oceanic dynamic phenomena. Sea ice. Oil pollution. Imprints of atmospheric phenomena on radar images. 2 Outlines II. Applications Microwave remote sensing of oceanic and atmospheric phenomena. Case studies. Multi-sensor approach. Currents, eddies, bottom topography, etc. Tropical and extratropical cyclones, intense mesoscale convective vortices, cold air outbreaks, etc. Remote sensing The ocean-atmosphere system is characterized by high temporal and spatial variability. The detailed study and monitoring of the Earth is the pressing problem. The use of remote sensing in different spectral bands to estimate geophysical fields is extremely successful. Electromagnetic radiation (EM) occurs as a continuum of wavelengths and frequencies from short wavelength, high frequency cosmic waves, to long wavelength, low frequency radio waves. The wavelengths that are of the greatest interest in remote sensing are visible and near infrared (IR) radiation in the range of 0.4-3 µm, (IR) radiation in the range of 3-14 µm and microwave radiation in the range of 1 mm – 1 m (frequency 0.3 – 300 GHz). 3 Electromagnetic spectrum, atmospheric transmission Two natural sources of radiation, the sun and Earth, are of particular importance in remote sensing. Spectral features of remote measurements Wavelength Microwave Infrared Visible range Regime Passive Active Passive Active Passive Active Day / Night + + + + - + Cloudiness + + - - - - Spatial low low and high medium high high-medium high resolution Penetration < mm – m < mm - m < mm < mm < mm (land) < mm depth > 100 m m (ice) (land) (land ice) < m – 20 m m (ice) (water) < m – 20 m (water) 30 [cm] Three measurements are used to describe EM waves: [GHz] wavelength () in µm, cm or m, frequency (ν) in hertz (Hz) and velocity (c) in m/s. 1 GHz = 109 Hz. 70 (degrees) 0.5 D 4 Sea Surface Height (SSH) Active measurements using microwave radar Pulse sent from satellite to earth, measure returtn time With appropriate processing and averaging, it is possible to calculate: Ocean currents, eddies (scales > 60-100 km) Deviations in ocean surface due to bathymetry Gradual sea level rise due to global waring Deviation in ocean surface due to internal physical variability (heat, salinity) 5 Improving Models •¼° spatial resolution •Hourly •Seasonal Simulations •Project Columbia (16 CPUs) •1 Week Wallclock Thanks to Project Columbia Visualization 13 6 Brightness temperature of the ocean-atmosphere system C TB MICROWAVE RADIOMETER ↓ T B atm h θ ↑ T B atm TB ocean(ν,θ)=κ(ν,θ) T0 Brightness temperature of the ocean-atmosphere system H H ( ,h)secdh T ( , ) ( , )T e ( )sec T (h)e h secdh B s 0 h ( ,h)secdh [1( , )]T (h) ( ,h)e 0 secdhe ( )sec 0 [1( , )]T C ( )e2 ( )sec TB is the brightness temperature at frequency , is the incidence angle, Ts is the thermodynamic temperature and is the emissivity of the sea surface, T(h) is the air temperature at height h, H is the satellite height, o (h)dh is the opacity (total absorption) of the atmosphere, 0 (h) is the absorption coefficient, C T = 2.69 + 0.003625 is the cosmic background radiation on the atmosphere top. 7 Spectra of the brightness temperature of the ocean-atmosphere system (curves 1) and the ocean at the lower (curves 2) and upper (curves 3) boundaries of the atmosphere. Solid lines – vertical polarization, dotted lines – horizontal polarization. Total water vapor content V = 59 kg/m2, total cloud liquid water content Q = 0.0 kg/m2 2 2 2 2 (black lines), V = 28 kg/m , Q = 0 kg/m (blue lines); Q = 0.6 kg/m , V = 61 kg/m (red lines). H20 O2 280 O2 H20 1 1 240 2 200 2 160 120 80 Brightness temperature, К Brightnesstemperature, 40 3 3 0 0 40 80 120 160 200 Frequency, GHz V ,H V ,H ( , ) V ,H ( , ) TB ( ,) TBocean(,)e TBatm( ,) TBatm( ,)[1 ( ,)]e V ,H 2 ( , ) TC [1 (,)]e V ,H V ,H TBocean(,) (,)TS is the brightness temperature of the ocean TBatm (, ) is the upwelling brightness temperature of the atmosphere TBatm (, ) is the downwelling brightness temperature of the atmosphere MICROWAVE RADIOMETER C TB ↓ T B atm h θ ↑ T B atm TB ocean(ν,θ)=κ(ν,θ)T0 8 Spectra of brightness temperature of the ocean-atmosphere system and the ocean at the lower TBocean = Ts and upper TBocean = Ts [exp(-sec) boundaries of the atmosphere for vertical and horizontal polarization calculated at various values of the atmospheric (V and Q) and oceanic (SST) parameters at incidence angle = 55. 300 H2O 1 O2 2 250 3 4 200 5 6 7 150 8 9 100 10 11 12 BRIGHTNESS TEMPERATURE (K) TEMPERATURE BRIGHTNESS 50 13 14 0 15 0 10 20 30 40 50 60 70 80 90 100 16 FREQUENCY (GHZ) Absorption by atmospheric gases and clouds (,h) = ox(,h) + wv(,h) + cl(,h) (,h) = F[, T(h), P(h), a (h), (h)] T(h), P(h), a (h) and (h) are vertical profiles of air temperature, atmospheric pressure, absolute humidity and cloud liquid water content ox(h) = oxreson(h) + oxnonreson(h) is molecular oxygen absorption, wv(h) = wvreson(h) + wvnonreson(h) is water vapor absorption, cl(h) is cloud absorption Resonance absorption: shape of resonance lines, line strength, dependence on P(h), collisions O2 - O2, O2 - N2, interaction between lines, etc. 9 Recent publications on WV absorption 1. Payne V.H., J.S. Delamere, K.E. Cady-Pereira, et al. Air-broadened half-widths of the 22- and 183-GHz water-vapor lines. IEEE TGRS, 2008, vol. 46, no 11, pp. 3601–3617. 2. Kneifel S., S. Crewell, U. Löhnert and J. Schween Investigating water vapor variability by ground-based microwave radiometry: Evaluation using airborne observations. IEEE Geoscience Rem. Sens. Lett. 2009, vol. 6, no. 1, pp. 157–161. 3. Turner D.D., M.P. Cadeddu, U. Löhnert et al. Modifications to the water vapor continuum in the microwave suggested by ground-based 150-GHz observations. IEEE TGRS, 2009, vol. 47, no. 10, pp. 3326-3337. 4. Cimini D., F. Nasir, E.R. Westwater et al. Comparison of groundbased millimeter- wave observations in the Arctic winter, IEEE TGRS, 2009, vol. 47, no. 9, pp. 3098–3106. 5. Payne V., K. Cady-Pereira and J.-L. Moncet Water vapor continuum absorption in the microwave. Abstracts of 11th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment. 1-4 March 2010. Washington, DC. USA. P. 58. GPS. Dependence between phase delay of electromagnetic waves and total water vapor content V. Del L = 0.6 cm/(kg/m2) Absorption by atmospheric gases and clouds (,h) = ox(,h) + wv(,h) + cl(,h) ox(h) is molecular oxygen absorption, wv (h) is water vapor absorption, cl(h) is cloud absorption () = ox() + wv() + cl() is total atmospheric absorption 100 Spectra of total absorption by 3 10 2 1 2 water vapor at V = 59 kg/m 4 4 1 2 0 20 40 60 80 100 120 140 160 180 200 and 28 kg/m (curves 1 and 2), 0,1 molecular oxygen (curve 3) 0,01 and clouds at Q = 0.6 kg/m2 Frequency, GHz o 0,001 and tcl = 0 C (curve 4). 10 Absorption by atmospheric gases and clouds (h)dh 0 () = ox() + wv() + cl() is total atmospheric absorption WV ( ) WV (,h)dh k[v,a(h)]V 0 V a(h)dh is total water vapor content 0 cl ( ) cl [,(h),T(h)]dh k[v,tcl ( )]Q 0 Q (h)dh is total cloud liquid water content 0 Cloud absorption 1 cl 0.06283 Im 0.1885 2 2 2 2 = + j is the complex dielectric permittivity of water, Im is an imagery part, is the cloud liquid water content 0.20 1.2 Total cloud liquid water (a) (b) content Q (h)dh 1.0 89.0 0.15 19.35 0.8 Dependence of total 85.5 cloud absorption with 0.10 0.6 Q = 1 kg/m2 on cloud 10.65 0.4 droplet temperature at 0.05 37.0 SSM/I, TMI and AMSR 0.2 22.24 frequencies of 6.9, 10.65 6.9 0.00 0.0 and 19.35 GHz (a), and -30 -20 -10 0 10 20 -30 -20 -10 0 10 20 22.24, 37.0, 85.5 and Cloud temperature, t C Cloud temperature, t C 89.0 GHz (b).