Chapter 11: Remote sensing A: Acoustic remote sensing (was chapter 9) B: Geostrophic transport estimates ∫ v dx = 1/fρ 0 [ p(x 2 ) – p(x 1 ) ] and with the thermal wind relation this become /dz ∫ v dx = -g/fρ 0 [ ρ(x 2 ) – ρ(x 1 ) ] Thus density profiles at the end points allow to obtain transport ∫ v dxdz . Bottom pressure gives reference layer velocity fluctuations. Here: example from
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C: Satellites (and aircraft)(most figures from Summerhayes&Thorpe “Oceanography: an illustrated guide
Spectrum used: visible to microwave, for microwaves have passive and active sensors
Non-scanning versus scanning
Geostationary versus orbiting
Space-time scales
SST observations
Ocean color observations
Synthetic aperture radar (SAR) observations
SAR example
SAR example
Waves and winds (scatterometer)
Altimetry
After the success of SEASAT, the newplanned altimetry missions were adustedto best complement the in-situ observations.Topex/Poseidon (T/P) was essentially designed for WOCE.
Rationale:• cm-accuracy sea-surface height • geostrophic surface flow relative to geoid• heat storage from large-scale steric effect• variability from 20-10000km, 20days-10years
Challenges and limitations:• geoid insufficient at <3000km • aliasing of tides at 62, 173,... days• aliasing of high-frequ. wind-forced variability• extrapolation to ocean interior• no coverage in polar (and ice-covered) regions• land motion of tide gauges for SL rise
Example result: extremely active time-dependence of the circulation (barotropic, baroclinic current systems,eddy motions, etc)
Quantified SSH and slope variance on all space/time scales globally
(C. Wunsch)
(D.Stammer)
Eddy contribution tomeridional heat flux:
Other results/achievements:• open-ocean tides measured globally to 2-3cm• surface heat-flux estimates on basin-scales from storage• observation of interannual variability (ENSO, circumpolar wave, etc)• kinetic energy of geostrophic currents in agreement with moorings• eddy energy helped to demonstrate that models need 0.1° resolution• agreement of T/P currents and ADCP data to 3-5cm/s• global test of Rossby wave speeds• global SL rise (calibrated with tide gauges) accurate to 0.5mm/yr• transports of baroclinic current systems (variability)• drove advances in earth´s gravity field• drove most of the work in assimilation• many more.....
(D. Stammer)
Missions at:http://airsea-www.jpl.nasa.gov/mission/missions.html(OLD) now see seperate ppt file.....
More about altimetry at:http://topex-www.jpl.nasa.gov/www.aviso.oceanobs.com/en/altimetry/index.html
More about scatterometer athttp://winds.jpl.nasa.gov/
Scatterometers: NSCAT (on Japanese ADEOS), QuickScat, SeaWinds (on ADEOS-II), ASCAT. Deliver vector wind (stress), sea ice, iceberg drift.
Radars: altimeter, SAR
Radiometer: AVHRR (advanced very high resolution radiometer), has several IR bands, can be used to estimate absorption in atmosphere, gives SST; Also in microwave now – SMMR (scanning multi-channel microwave radiometer), passive, also yields ice cover and humidity
SSM/I: special sensor microwave imager, gives only wind speed (not direction), 4 bands, precipitation
CZCS: coastal zone color scanner (on Nimbus satellite), many visible channels
More neat stuff, e.g. “Iridium flares” atwww.heavens-above.com/
Sea surface height (SSH) consists of - the steric (dynamic height Hdyn) contribution of T and S - a barotropic flow component (reference level pressure Pref)
Symbolically SSH = Pref + Hdyn = SSH’ + SSH
Altimetry has good spatial and temporal coverage but cannot determine
- steric and non-steric components- mean SSH field (relative to geoid)- T and S contributions (spiciness)- interior structure (vertical distribution) of Hdyn
ARGO data can help resolve these issues
altimetryFloat profiles
Symbolically SSH = Pref + Hdyn = SSH’ + SSH
scatter is a measurefor non-stericcontributions(plus errors)