1) Internal waves are gravity waves that oscillate within the layers of a stratified fluid like the ocean. They can be initiated by tides, wind stress, underwater topography, and boat/submarine movement. 2) MODIS satellite imagery is used to detect internal waves in the North Indian Ocean through visualization techniques like sunglint and image enhancement. Shifting bands of light and dark are identified as propagating internal waves. 3) Internal waves play an important role in ocean circulation, heat distribution, and plankton distribution, and can affect underwater technology, sound propagation, and marine infrastructure. While more expensive SAR images can clearly detect internal waves, MODIS provides freely available imagery for their detection and analysis.

1. Divya Basuti
Detection and Analysis of
Internal Waves Using Satellite
Imagery of the North Indian
Ocean
Institute of Science and Technology, JNTU Hyderabad
Center for Environment
Environmental Geomatics
Supervisor: Dr. N. Srinivasa Rao, Scientist and In charge, SDAPD, INCOIS

2. The Ocean: The Final Frontier?

3. Introduction
Internal waves are gravity waves that oscillate within rather
than on the surface of a fluid medium.
Fig: Internal waves near Strait of Gibraltar

4. For internal waves to exist, the fluid must be stratified.
Stratification : Density decreases continuously with height
due to changes in temperature or salinity or both.
Fig: Layers of ocean according to temperature and density

5. The layered nature of the ocean causes the shallower water
which is warmer, less salty, and lighter to overlay deeper
water which is colder, saltier, and denser.
Internal waves forms at the interface between the layers
Fig: Internal wave formation at the interface of the two different densities

6. Internal waves can be initiated
and set in motion by
the following:
•Tides
•Wind stress
•Boats and submarine movement
•Currents moving over underwater
topography (ridges)
Fig: Tides
Fig: Boat and Submarine movement
Fig: Wind Stress
Fig: Underwater ridges

7. Fig: Dead water

8. Data used:
Level 1B data at 250 M from the Moderate Resolution
Imaging Spectroradiometer (MODIS) onboard the Aqua
and Terra satellites.
Fig: MODIS onboard AQUA satellite
Methodology

9. The MODIS level 1B data product at 250M resolution can be
downloaded from the MODIS website in HDF.
Fig: MODIS website

10. They are converted into TIFF using the MODIS Swath
Reprojection Tool available for download at the NASA website
Fig: MODIS swath reprojection Tool

11. The TIFF images can now be used in ERDAS IMAGINE software
after they are layer stacked and saved with an .img extension
Fig: Erdas Imagine software

12. Visualization:
Reflectance pattern of sunlight off the ocean surface
(sunglint) to be used to identify high frequency Internal wave.
Fig: Sunglint image of Indian Ocean

13. In absence of sunglint image processing methods such as
contrast stretching can also be used to visualize internal
waves.
Fig: Before and after Contrast stretching

14. Image Enhancement:
Fig. False color composite

15. Fig. Histogram Stretching

16. Pre Image Enhancement Post Image Enhancement
Fig: Before and after Image Enhancement using Histogram stretching technique

17. Identification:
The waves manifest themselves as alternating bands
of light and dark quasilinear strips that remain coherent
over tens to hundreds of kilometers lasting several hours.
Fig: Visualization of internal waves by observing the alternating dark and light strips

19. AQUA-MODIS
13:35 Hrs
Fig: Shift in position of wave packet between TERRA MODIS pass and AQUA MODIS pass.
TERRA-MODIS
10:30 Hrs

20. Fig: Wave propagate and persists for several hours, Establishing that they are internal waves

21. Why study Internal waves?
Play a role in:
•Ocean circulation
•Heat distribution
•Plankton distribution
Affect the Performance of:
•Underwater technology
•Acoustic communication
•Marine cabling
•Submerged vessels and vehicles
•Underwater sound propagation
Fig: ocean circulation
Fig: submarine communication through SONAR
Fig: plankton distribution

22. Advantage of using MODIS data instead of SAR images in the
study
Although IWs can be observed easily in SAR, these images are
usually very expensive.
Therefore in this project, We use the satellite ocean colour
images, at no cost and easily available to the public, to detect
IWs.
Fig: SAR image Fig: MODIS True Color Image

23. Conclusion:
Image enhancement techniques such as contrast
stretching have been used in this study, in conjunction
with the sunglint effect to better visualize internal waves.

24. Limitations and Recommendations:
The obstruction of desired feature by clouds is a very
common problem encounter during detection of internal
waves, as cloud cover is seen on about 67 percent of the
Earth's surface at any given time, and less than 10 percent
of the skies over the ocean are clear. In further studies, this
can be overcome by using the cloud mask algorithm.

25. Bibliography
•seafriends.org.nz/oceans/waves.htm
•earthobservatory.nasa.gov
•incois.gov.in
•chapter7.tulaneuniversity.com
•taylorandfrancis.com
•http://www.nasa.gov/centers/goddard
•http://modis.gsfc.nasa.gov/