RADAR PHOTO SMOOTH OCEAN LONG WAVES. Introduction

Transcription

1 Formation of radar and visible contrasts from the water surface RADAR PHOTO SMOOTH OCEAN SHORT WAVES Beal, 1994 LONG WAVES INTERNAL WAVES Introduction Satellite RAR and SAR have a high potential to study the mesoand submesoscale atmospheric andoceanic phenomena and sea ice. This is due to independence of radar imagery from cloudiness high spatial resolution sensitivity of the radar backscatter to the sea surface roughness variations. Roughness variations result from modulation of the sea surface roughness by variable currents and surfactants. The imprints of the atmospheric vortices with horizontal (rolls) and vertical (open and closed cells) and other atmospheric phenomena accompanied by sea surface wind variations as well as oceanic eddies and eddy chains, island wakes, fronts, currents, internal waves, sea ice etc. are revealed on radar images due to their brightness contrasts and distinctive spatial characteristics. A high spatial resolution of SAR data makes possible studying sea surface water circulation in a range from hundreds meters to several tens kilometers. 1

2 Physical background Appearance of the oceanic phenomena on a radar image is caused by modulation of the Bragg-scale wind waves by the variable currents. The corresponding areas represent the anomalous states of the sea surface as opposite to a normal state when their roughness is determined by the surface wind stress only. The following MECHANISMS can make a contribution to the radar signatures of the sea surface during ice-free period: CURRENT SHEAR at the boundary between the water masses having different velocities modulates the small-scale roughness due to wave-current interaction. SURFACE-ACTIVE FILMS which are accumulated in the convergent zones damp the capillary-gravity waves. DECREASED STABILITY of the atmospheric boundary layer above the warm current waters compared to the cold off shore waters leads to the increase of the sea surface roughness of current waters. CHANGE OF THE AIR VELOCITY relative to the moving and quit water surface is accompanied by the corresponding change of the sea surface roughness. The atmospheric phenomena are imprinted on the RAR and SAR images since they modulate the wind stress at the sea surface. In turn, it depends on wind speed and stability of the boundary layer of the atmosphere (on the temperature difference between the water and the air). Formation of imprints of the phenomena is determined by environmental conditions (wind speed, current velocity, etc.) and a possibility to observe them depends on radar characteristics. Oceanic and atmospheric parameters and phenomena influencing on backscatter and manifesting themselves on radar images 2

3 Kosmos-1500 and Ocean series satellites Real Aperture Radars ( ) Wavelength 5.6 cm Polarization VV Resolution 1-2 km Swath width 460 km Incidence angle SENSOR CHARACTERISTICS Satellite ERS-1/2 ENVISAT SENSOR SAR ASAR Frequency, GHz Wavelength, cm Polarization VV VV, HH Incidence angle, deg (variable) Swath width, km Ground resolution, m 25 x x x150 European Remote Sensing Satellite ERS-1 was launched on 17 July 1991, ERS-2 was launched on 21 April 1995 and Envisat was launched on 1 March

4 ALOS PALSAR ALOS was launched on January 2006 PALSAR characteristics Regime Fine ScanSAR Polarimetric Polarization HH, HV HH + HV VV+VH HH, VV HH + HV + VV + VH Incident angle Pixel size, m Swath width, km PALSAR operates at wavelengh of 23.6 cm QuikSCAT scatterometer, Terra and Aqua MODIS spectroradiometer, Aqua AMSR-E microwave radiometer, surface analysis maps, bottom topography, etc. Aqua QuikSCAT 4

5 Meteorological scales and satellite sensors Orlanski (1975) scale Macro α (planetary scale) Macro β (synoptic scale) Meso α Meso β Meso γ Micro α Micro β Micro γ Spatial scale km km km km 2 20 km Sensors ASAR, AMSR-E, PALSAR ASAR, AMSR-E, PALSAR AMSR-E, ASAR, PALSAR m ASAR, PALSAR m ASAR, PALSAR 2 20 m Ancillary information SeaWinds, AVHRR, MODIS, Landsat, weather maps Orlanski, I., 1975: A rational subdivision of scales for atmospheric processes. Bull. Amer. Meteor. Soc., 56, Mesoscale convective cells Open cells which are defined by clouds in the upward motion along the edges of honeycomb-shaped cells, with less cloudy subsiding air in their centers. The closed cells have cloudy centers and cloud-free edges. open closed SPOT-2, 31 December 1996 Landsat-TM, 4 April

6 Global distribution of mesoscale cellular convection Okhotsk Sea Japan Sea NW Pacifi c Agee, 1987 (a) (b) 11 November 2003 Okhotsk Sea Ice 7 December 2003 Sakhalin Mesoscale convective rolls and cells on satellite images acquired on 10 January 2007 (a) at 11:39 UTC by NOAA-17 AVHRR and (b) at 11:46 UTC by Envisat ASAR Hokkaido 6

7 Organized structures in the marine boundary layer of the atmosphere. Convective rolls and cells ice ice Aqua MODIS Terra ice MOD IS 01:10 UTC ALOS PALSAR ice ALOS PALS AR 01:02 UTC ice ice Aqua AMSR-E, Tb(89H) Aqua ice AMS R-E 02:30 UTC ice Hokkaido Hokkaido Hokkaid o Roll convection Simulations of radar backscatter variations. C-band, VV polarization, incidence angle 30. Synoptic surface wind speed W syn = 6 m/s, amplitudes of mesoscale wind speed variations A x = 0.5 m/s, A y = 0.3 m/s. 7

8 3D display of the specific humidity field from the simulation at 10 h. The x z plane is at y = 100 km; the x y plane is at z = 25 m; three y z planes are at x = 150 km, x = 250 km and x = 350 km separately. A.Q. Liu et al. The effect of the sea ice zone on the develop-ment of boundary-layer roll clouds during cold air outbreaks. Boundary-Layer Meteorology Vol P Secondary flow development at 10 h over the sea-ice zone (a) x =90km (45% sea ice), (b) x =130km (18% sea ice) and (c) x =170km (open water). The specific humidity field (g kg 1) is shaded, the cloud liquid water mixing ratio (g kg 1) is contoured with contour interval 0.05 g kg 1 and the velocity in the y z plane is indicated by the vectors (only plotted every fourth grid in y direction and every third grid in z direction with abs (w)>0.1m s 1). 8

9 Kamchatka Kamchatka 2011/11/30 Brightness temperatures at 89 GHz, H-pol during cold air outbreak on 20 December A; 02:30 UTC K 105D; 16:30 UTC K Kamchatka Brightness temperature at 89 GHz, H-pol during cold air outbreak on 21 Dec 2002 at 01:30 UTC K 9

10 Open cells. 21 December 2002, 15:30 UTC, 89 GHz, H-pol ΔT b = T bcl T bo = a o Q + a 1 ΔV + a 2 ΔW 48.7 N 47.8 N 46.3 N Mesoscale convective open cells Kamchatka K K 21 December 2002, 15:30 UTC 89 GHz, H-pol 10

11 Kamchatka 2011/11/30 Imprints of open cells on satellite RAR and SAR images 8 February 2000 Ocean, RAR 20 Dec 2002, 04:21 UTC Envisat ASAR (а) (b) (c) (d) (e) (f) Open cell. Fields of parameters Synoptic wind W = 5 m/s Wind speed Water vapor Cloud liquid water 11

12 Open cell. Wide cloud ring. Brightness temperatures H-pol Synoptic wind W = 7 m/s H-pol V-pol Natural (biogenic) slicks ERS-1 SAR. 22 September 1995 The Pacific Ocean to the south of Kuril Islands System of dense packed spiral eddies. Monomolecular biogenic films serve as an indicator of the sea surface circulation at wind speed of 2-6 m/s. Spiral eddies are registered due to their negative radar contrast against the background 12

13 Envisat ASAR 3 2 (a) (b) QuikSCAT 1 5 A 4 B ESA 2004 ASAR image HH-pol, 11:46 UTC (a) and QuikScat-derived wind field at 10:02 UTC on 1 December 2004 (b). Bands 1 and field 2 has negative radar contrast relative to the ice-free sea surface due to ice grease. Ice field 3 is located in area where wind speed lower that to the west of it. Brightness of area 3 is higher than in areas 1 and 2, likely due to pancake ice. A narrow dark band surrounding area 3 consists very likely of grease ice. Grease ice is clearly seen on upwind side of ice massive 4. Its total area km2 grease ice area is 1600 km2. Envisat ASAR 1 Dec 2004, 11:46 UTC 4 Recent Langmuir circulation research has demonstrated a potential role for this phenomenon in global climate models. ESA

14 1 8 Sakhalin Hokkaid o 7 7 ALOS PALSAR PALSAR image of the Southwest Okhotsk Sea acquired on 19 January 2008 at 01:15 UTC. 1 Rishiri Island, 2 Cape Soya, 3 - Cape Krilion, 4 Cape Aniva, 5 La Perouse Strait, 6 Aniva Bay, 7 strong winds, 8 squall line, 9 - thin ice. ALOS PALSAR Terra MODIS Sakhalin Hokkaido 01:15 UTC 01:05 UTC 14

15 (а) Aniva Bay. Ice eddies. (б) Hokkaido Hokkaido ALOS PALSAR. February 2009 Ice eddies and bands (a) (c) (b) (a) ERS SAR quick look image obtained on 9 March 1992 with cyclonic ice-ocean eddy street near Primorye coast. (b) ERS SAR quick look image obtained on 21 March 1992 and showing an ice band with the wave-like features. (c) The location of the ERS SAR frames in the Tartar strait. ESA

16 Eddies, eddies everywhere Typhoon Megi Envisat ASAR 17 October 01:22 UTC P min = 910 mb Processed by Yu. Kuslyakina (POI FEB RAS) SENSOR ASAR Frequency, GHz 5.3 Wavelength, cm 5.6 Polarization VV, HH Incidence angle, deg Swath width, km Ground resolution, m 25 x x150 16

17 Rain cells Sensing direction Eye and eyewall P min = 910 mb Rain band, squalls 01:22 UTC Pmin = 910 mb Envisat ASAR Luzon Taiwan MetOp ASCAR 13:12 UTC Pmin = 895 mb 17

18 Cyclonic eddies (1 to 6), warm water flows (7 and 8) and oil pollution traces (9) in the Japan Sea, east of Korea, on 14 April 2004: (a) Envisat ASAR image, at 01:28 UTC, and (b) NOAA AVHRR infrared image, at 15:20 UTC. The dark rectangle in (b) marks the boundaries of ASAR image. Sand bars, fronts, island wake, ships and oil spills on ERS-1 SAR image for 29 November Bathymetry of the Taiwan Strait H.-R. Liao et al. (2008). Marine Geology. V. 248, pp

19 Eddies, internal waves ships and oil spills on Envisat ASAR image taken on 20 Dec 2008 April 2009 Okhotsk Sea. Spiral eddies to the North of Kuril Islands Simushir WB 1 ScanSAR 5-beam o HH 10:30 UTC 19

20 Schematic summary of the main hydrographic features of the Kuroshio-Oyashio Extension Region OY: Oyashio current, OYI: southward intrusion of the Oyashio, WCR: warm-core ring, CCR: cold-core ring, CWA: coldwater area, KE: Kuroshio Extension, KBF: Kuroshio bifurcation front, TWC: Tsugaru Warm Current. S. Itoh and I. Yasuda, Characteristics of mesoscale eddies in the Kuroshio Oyashio Extension Region detected from the distribution of the Sea Surface Height Anomaly, J. Phys. Oceanography, 2010, vol. 40, Schematic summary of the behavior of mesoscale eddies in the Kuroshio-Oyashio Extension Region Thin dashed arrows indicate movement directions. Flows of the Oyashio and the KE, the SAF, and the SAB are shown by solid gray lines; the deepest part of the Japan and Kuril Kamchatka Trenches is depicted by a dashed gray line. WCR, CCR, KE, SAF, SAB, and TWC represent warm-core ring, cold core ring, the Kuroshio Extension, Subarctic Front, subarctic boundary, and the Tsugaru Warm Current, respectively. (Itoh and Yasuda, 2010). 20

21 Temperature 2011/11/30 Hokkaido Itoh,Yasuda, and Ueno, PICES, 2010 Honshu Hokkaido Kuroshio-Oyashio transition zone Hokkaido NOAA-10 AVHRR infrared image acquired on 30 April 1987 (left) and Kosmos-1500 Real Aperture Radar image Warm eddy Cold Oyashio water Distance, km Resolution 1-2 km Mitnik L.M. and V.B. Lobanov (1991), Reflection of oceanic fronts on satellite radar images, Oceanography of Asian Marginal Seas, Kenzo Takano, Ed., Amsterdam, Elsevier, pp

22 4 1 Kuroshio-Oyashio and synoptic eddies 3 Okhotsk Sea 460 km 2 Resolution 1-2 km Hokkaido 1 Okhotsk Sea Okean-7 X-band Real Aperture Radar (RAR) and NOAA AVHRRderived SST. 20 November White rectangle marks the boundaries of RAR image. Wind speed to the south of Kuril Islands was 5-6 m/s. Anticyclonic eddy 1, warm Kuroshio waters 2 and cold Oyashio waters 2 are revealed due to high radar contrast. Fine details of SST field (such as warm streamer 4 and others) are clearly depicted on the RAR image. SST contrasts reach 12 C at the eddy boundary. ALOS PALSAR. Anticyclonic eddy (а) (б) (б) (a) (в) 6 (b) Hokkaido Honshu 290 км Honshu PALSAR image acquired on 18 April 2009 at 01:10 UTC; (b) sea surface temperature map for the same day submitted by Fishery Research Association. Red rectangle marks the boundaries of PALSAR image. 1 warm waters, 2- cold waters, 3 warm streamer, 4-6 and 5 cold small eddies, 6 warm small eddy. 22

23 Aqua MODIS. 19 April 2009, 03:40 UTC (c) Infrared image (31-st channel) and (d) chl-a field (c) (d) Hokkaido Honshu Honshu 1 warm waters, 2- cold waters, 3 warm streamer, 4 and 5 cold small eddies, 6 warm small eddy. Red dotted rectangle marks the boundaries of PALSAR image. Conclusion Satellite radar images register the sea surface roughness variations with space scales from several tens till several tens kilometers. Various structures on the sea surface caused by dynamic processes in the upper layer of the ocean are observed at this range of scales. Organized variations of the sea surface wind are observed under roll and cell convection in the atmosphere and also under interaction of air flow with obstacles (atmospheric gravity waves, vortex chains, wind shadows, etc). Visible and IR images, passive microwave and scatterometer data as well as the results of modeling are used to improve interpretation of the brightness variations on radar images, construct 3D-patterns of the atmospheric and oceanic processes and advance their theoretical description. 23

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