Drift Ice Detection by HF radar off Mombetsu

Transcription

1 Drift Ice Detection by HF radar off Mombetsu 凘 氷解而流也 Wei Zhang 1, Naoto Ebuchi 1, Brian Emery 2 and Hiroto Abe 1 1 Institute of Low Temperature Science, Hokkaido University 1 2 Marine Science Institute, University of California Santa Barbara

2 Ocean Radar in Mombetsu Russia China Sea of Okhotsk Japan 2

3 CODAR SeaSonde Radar Stations Waveform: FMICW Center frequency: MHz Detection range: 46.5 km Range resolution: 1.5 km Azimuth resolution: 5 deg.

4 Example of Observed Snapshot 13h00m (JST) 17 Oct. 14 Real-time current maps are available from our web site.

5 Power (db) Range (km) Observed Doppler Spectrum -85 CSS_MOMB_13_11_26_00.cs4 Antenna 3 Color Map -90 First Order -95 First Order 45 CSS_MOMB_13_11_26_10.cs4 Antenna 3 Color Map

6 Power (db) Current Information First Order f First Order Wind: Radial to radar Bearing: -15 o ~ 30 o Current SNR: 30 db Current Vel.: 0-30cm/s Radar Freq.: 24.56MHz Antenna: Cross-loop Monopole

7 Hourly Surface Current Fields HF ocean radar clearly capture the current variation

8 Drift Ice off Mombetsu Surface current circulation by drift buoy

9 Observed Range-Doppler Spectrum CSS_MOMB_13_11_01_.cs4 Antenna 3 Color Map CSA_MOMB_14_02_11_00.cs Antenna 3 Color Map Sea Ice First Order Range (km) 1-90 First Order -0-1 Mount./Noise? Range (km)

10 Radar Equation Description of the relationship of transmitted power, received power and the range P r Received Power P t Transmitted Power P r = P tg t G r σλ 2 (4π) 3 d 4 L p 2 G t Transmitted Gain G r Received Gain σ Radar Cross Section d Detected Range λ Radio Wavelength Lp Path Loss Earth Surface

11 Radar Cross Section Type Average RCS Freq. Iceberg 0.06*contour area 2-30 MHz Bergy bit 0.07*contour area 5-30 MHz Growler 0.08*contour area -30MHz Figures, Walsh et al. (1986); Table, Haykin et al. (1994) 11

12 Path Loss [db] Radio Path Loss Simulation L p d L p d = log ( P r P t ) = log f MHz + log(e μν/m ) E μν/m Electrical field strength f MHz Radio frequency in MHz HF radio over Sea Water 5 MHz 15 MHz 25 MHz Range [km] 12

13 Path Loss [db] Mixed Path Loss Simulation Sea Ice vs. Sea Water Sea Water Sea Ice Mixed Path Range [km] f 0 = MHz Sea Water: σ w = 5 S/m ε w /ε 0 = 80 Sea Ice: σ i = 1 S/m ε i /ε 0 = 6 Mixed Path: Sea Water: Km Sea Ice : Km The HF radio wave over sea ice decrease faster than over sea water. 13

14 Range (km) Range (km) Range (km) Range (km) Sea water/mixed path Example CSA_MOMB_14_02_07_2300.cs Antenna 3 Color Map CSA_MOMB_14_02_28_0000.cs Antenna 3 Color Map CSA_MOMB_14_02_25_0500.cs Antenna 3 Color Map CSA_MOMB_14_02_26_20.cs Antenna 3 Color Map

15 Range (km) Range (km) Range (km) Range (km) Sea Ice Path Example CSA_MOMB_14_02_08_1600.cs Antenna 3 Color Map CSA_MOMB_14_02_12_0500.cs Antenna 3 Color Map CSA_MOMB_14_02_08_1500.cs Antenna 3 Color Map CSA_MOMB_14_02_11_0500.cs Antenna 3 Color Map

16 Power (db) Power (db) Doppler Simulation Sea Ice with Current First Order -5 Sea Ice First Order Sea Ice Only Current SNR: 30 db Current Vel.: 0-30cm/s Sea Ice SNR: 15 db Sea Ice Vel.: -25cm/s Radar Freq.: 24.56MHz Antenna: Cross-loop Monopole

17 Power (db) Radial Velocity f Target Radial Velocity 2V r c = Δf f 0 V r : Ice radial velocity f: Ice Doppler shift f 0 : Radar frequency c : light speed

18 Direction Finding MUSIC (MUltiple SIgnal Classification) algorithm Single Case Dual Case Angle (deg.) Angle (deg.) 1. Assumed no more than two azimuth angles at one sea ice Doppler point; 2. Angle numbers are determined by signal and noise powers. 18

19 Current and drift Ice Radial Velocity Map Current and Ice Map: MOMB_14_02_11_00 36' 32' 44 o N 28.00' 24' MOMB 0 cm s -1 ' Current Ice 12' 18' 143 o E 24.00' 30' 36' Drift ice velocity is roughly consistent with nearby current. 19

20 Application of Ice Radial Velocity Relationship of Wind, Ice and Current: v dif = v ice vcur v dif = αcosθu + αsinθv Least Square Method v ice ice radial velocity vcur average radial current velocity α speed ratio θ turning angle W(U, V) wind vector f α, θ = min (α,θ) [v dif αcosθu αsinθv ] Usually, the wind to ice speed ratio is 2%.

21 Wind to Ice Drift Parameter 36' 32' 44 o N 28.00' 24' ' Current and Ice Map: MOMB_14_02_09_20 0 cm s -1 MOMB Current Ice Wind 12' 18' 143 o E 24.00' 30' 36' Green Distance : 13.5 Km Turning angle: 51 o Speed ratio: 2 % Data points: 1 Cyan Distance : 6 Km Turning angle: 54 o Speed ratio: 1.43% Data points: 4 Wind to ice drift parameters are reasonable by using ice and current radial data from HF ocean radar.

22 Summary HF ocean can detect drift ice, and obtain bearing angle and radial velocity. Generally, drift ice detection range by HF ocean radar is about Km Wind to ice drift parameters calculated from sea ice and current HF ocean radar are reasonable, and turning angle is about 50 degree, speed ratio is 1.4% ~ 2%. 22

23 Citation Reference Walsh et al. (1986), Remote sensing of icebergs by ground-wave Doppler radar. Haykin et al. (1994), [M] Remote Sensing of Sea Ice and Icebergs. 23