Remote Sensing C 2013 Anand Gnanadesikan Johns Hopkins University

A little about me… Physical oceanographer by training. Currently on the faculty at JHU in the Department of Earth and Planetary Sciences, Former parent/coach.

Key Points Remote sensing covers how we explore the atmosphere and hydrosphere from space. Key points –Basic physics –Types of sensors –Main missions –Image analysis –Key phenomena

How to prepare Although rules state that only five sheets of paper are allowed in competition… Build a binder! –Not just xeroxing and printing –Writing up notes on different topics Five sheets should be a summary of this binder.

Key skills How to read a plot with different axes (log- log, time series) How to go from a contour plot to a line plot. How to use spectral characteristics to justify an algorithm.

Types of sensors Electromagnetic –Active (shoot radiation at planet, look at return) –Passive (use radiation coming off planet) Gravitational –Use changes in acceleration to get at distribution of mass.

Key concept 1: Electromagnetic spectrum Difference between microwave, IR, visible. What it means to say that we sense things at different wavelengths. How different wavelengths might be combined to learn about

Example: Normalized Difference Vegetation Index (NDVI) measuring_vegetation_2.php

Key concept 2- Black body radiation This implies we can find “brightness” temperatures by looking at emitted radiation at different wavelengths. “Cooler” temperatures either correspond to lower emissivity, or cooler temperatures. Q=  T 4

Example: NOAA Outgoing longwave radiation product Very high values over Sahara. Very low values at about 15N, 50W (tropical cyclone)

Example: TMI Sea surface temperature At wavelength of about 3 cm- can see through clouds!

Key concept 3- Polarization Electric fields would push test charge up and down- vertical polarization. Electric fields would push test charge right and left horizontal polarization. Because water has free charges, it tends to resist forming electric field gradients along surface. Light emitted and reflected from water tends to be vertically polarized.

Result: If we use polarizing filters, open water looks dark in microwave horizontal band. Cavalieri et al., JGR, 1984

Microwave brightness images In this band, areas that are orange on right and blue at left are open water. From combining images in different bands we can get ice cover.

Key concept 4:Atmospheric absorption Transparency of the atmosphere varies Where would we not look for signal? Where might we look for ozone?

Key concept 4: Scatterometry Many radars use the concept of Bragg scattering, which requires “resonance” between a scatterer and the wavelength of incoming radiation. The intensity of the scattering tells you about the “roughness” of the surface at that wavelength. agg_scattering.htm

Example Because winds roughen the surface, one can retrieve wind speeds from scatterometry. Shown at left is Hurricane Dolly (2008)

Key concept 6: Gravimetry Two satellites spaced 220 km apart are tugged on differently by more/less massive objects. Changes in this tug over time reflect change in mass distribution.

Example- Mass changes from water redistribution

Further resources…. Will be posted on my web page I am also working with the coordinator for Dynamic Planet and will be posting Glaciology resources on this site.