- Start and Map pages
- MainSequence 1: Cloud chambers and cosmic rays
- MainSequence 2: The stardust hypothesis
- MainSequence 3: Little toy universes
- MainSequence 4: The photoelectric effect
- MainSequence 5: Casting dice
- MainSequence 6: A physical calculation
- MainSequence 7: Photon deflection
- MainSequence 8: Electromagnetic prisms
- MainSequence 9: Some polar science
- MainSequence 10: Watershed hydrology
- Main Sequence 11: Lunar shenanigans
- Main Sequence 12: An infinite quantity of mathematics
- Main Sequence 13: Remote sensing of the environment
- Main Sequence 14: The Rock, some math for a younger person
Data in environmental science presents a challenge, contributing as it does to scientific insight. Suh data typically derives from laboratory analysis, field observation (including in situ sensors), remote sensing and modeling. Not surprisingly: The more ambitious the research scope, the more correspondingly difficult tends to be the data challenge.
This page takes a look at remote sensing, particularly what can be done in the cryosphere using imaging radar, sometimes called Synthetic Aperture Radar or SAR for short. A SAR uses a microwave antenna to broadcast its own source of illumination like a camera with a flash bulb. In contrast to visible light, however, a SAR sends and receives photons with a centimeter-scale wavelength, and it records the reflected energy in terms of both brightness and (astoundingly) a second value that represents a fraction of that wavelength. I'll write more on this below, but for now I want to complete these introductory ideas.
Illuminating the ground with microwaves can sound simple enough in principle but the task of deriving valuable information about that ground is still a complicated and often arduous one. For example: Calibrating radar echoes to an absolute reflectivity may involve constructing bright target structures in the landscape; which sounds like it defeats the purpose of remote sensing since you must go out into the fieldwork. And this can be difficult for example on Venus so the expense report is always a big hassle. (For historical reasons here is a link to a video on methods for deploying a calibration reflectors for a SAR.)
As with many technology-driven advances in data gathering, for SAR we can ask the very important question: At what point can a scientist use the end-result without having to know where it came from? This question is secondary to one more immediate: Once you have an operational instrument (SAR): What can you do with it? This page attempts to look at both of these questions, so to conclude the introduction I will write them out again:
- What information can a SAR give us about ice on the earth's surface?
- What is necessary to get this information without knowing what a SAR is or how it works?
Preamble on SAR and glacier transport of fresh water
Glaciers transport fresh water downhill, in most cases to the ocean, in great volume and at several different time scales. Perhaps incongruously glaciers transport water fastest when they are melting since melt water is mobile while ice is not. Ice in a glacier moves slowly in comparison but the volume of water transported to the ocean by glaciers each year as ice is still tremendous, owing to the large collection of such glaciers distributed around the earth, particularly southern South America, Alaska, Greenland, and in Antarctica.
By far the most remarkable contribution of SAR to the study of ice has been the characterization of glacier flow. I am going to describe this contribution in the "old fashioned" way that was pioneered by Andy Gabriel in the 1980s at NASA's Jet Propulsion Laboratory, and this means introducing a explaining -- to a degree -- related notions of coherent antennas and phase. The reason for being old fashioned is twofold if you are kind enough not to include "lazizness" among the motivations. First it attempts to illustrate the process of discovery in research, and second it will lead to the second section which examines getting to results without having to worry about where they came from.