2. Internal Waves: Lesson Overview

Aims and objectives

This lesson is a general introduction to internal waves and aims to teach established techniques for interpreting internal wave signatures. It focusses primarily on Synthetic Aperture Radar examples of internal solitary wave packets. By the end of this section you should be able to

• recognise internal wave signatures in ENVISAT ASAR and ERS SAR data,
• make simple estimates of internal wave characteristics such as average internal packet speed, crest length and wavelength,
• understand some of the mechanisms by which IWs modify surface ripples and thus the sea surface roughness as observed in SAR images, including the aggregation of surfactant films due to the surface currents produced by internal waves,
• distinguish between internal solitary waves of elevation and depression.

Section content

1. Case study 1: Mozambique shelf.
   • Detecting internal waves off Mozambique
   • Measuring wave length
   • Calculating internal wave velocity
2. Case study 2: South China Sea.
   • IWs in the South China Sea
3. Case study 3: Gulf of Cadiz, Spain.
   • Polarity of internal wave SAR signatures

Images used in this section

• ASA_WSM_1CNPDK20030306_~.N1
  This is a hierarchical format ASAR image of the Mozambique region taken on 06/03/2003 at 07:16:52 (UTC) in WSM mode.
• ASA_WSM_1PNUPA20040128_~.N1
  This is a hierarchical format ASAR image of the Mozambique region taken on 28/01/2004 at 07:08:25 (UTC) in WSM mode.
• ASA_WSM_1PPIPA20030815_~.N1
  This is a hierarchical format ASAR image of the South China Sea taken on 15/08/2003 at 02:10:56 (UTC) in WSM mode.
• P025_871.8x8
  This is a flat file SAR image off the coast of Cadiz, Spain taken on 23/07/1998 at 11:10:56 (UTC) in PRI mode.

Note: The term ASAR WSM represents Advanced Synthetic Aperture Radar Wide Swath Mode.
The ASAR images used in this lesson have a spatial resolution of 75 m and cover an area of about 400x400 km. The ERS SAR images have a spatial resolution of 30m and cover about 30km x 30 km.