Public Lab Research note


by cfastie | October 25, 2013 16:43 25 Oct 16:43 | #9548 | #9548

Image above: Taking off from San Francisco and landing in Chicago on Monday. I think I was very lucky to get good views of both cities on one flight.

On the way home from the GSoC Mentor Summit my window seat was just far enough in front of the wing to take some photos and Infragrams. I had the same cameras as on the flight to San Francisco and produced NBG and NDVI images the same way. I freely altered the photos and NBG images in Photoshop to highlight vegetation patterns, although the NDVI images are straight out of the Fiji plugin.

Most things worth photographing from 35,000 feet are easy to find in Google Earth, so I was able to reconstruct the flight path from the photos included here. Early on, this path was 170 miles north of Friday's westbound flight, so I got to see different things. The western bias is because it was clear only for that part of the flight. I was on the north side of the plane with the sun behind me which makes a huge difference in photo quality.


I was treated to this scene as soon as we took off. Around the shadow of the Boeing 757-300 is a glory. Glories are formed when the sunlight coming from directly behind you interacts with water droplets in front of you and is redirected back to you with some color separation. That is also a description of a rainbow, but glories are not due to refraction. The most amazing thing about glories is that nobody knows how they form and that classical wave tunneling is suspected. The exact center of the glory is my antisolar point, confirming my seat location just in front of the wing. The pilot would have seen a different juxtaposition of shadow and glory.

A glory later in the flight captured with an unmodified Canon S95 (left) and then with the infrablue A810 (right). There is no plane shadow with these glories because the plane is many thousands of feet away from the clouds and its shadow cone does not reach them. I thought I might learn something about infrared light or wave tunneling from the infrablue photo, but I didn't. Had I been able to control for focal length, I might have learned whether an infrared glory is the same size as a visible light glory, but I wasn't.


Center pivot irrigation circles south of Bluewing Flat, NV. The NBG image displays the near infrared light as red, and the crops are conspicuous because nothing in the scene reflects as much NIR as growing crops. The green background is where very little NIR was captured by the infrablue photo. The NDVI image does a similar job distinguishing irrigated crops from desert vegetation, but then a regular color photo also does a darn good job in this situation.


Center pivot irrigation circles near Unionville, NV. Although the NBG image rivals the NDVI image for discriminating between crops and desert, the NBG image required more tweaking to highlight that distinction. So the NDVI approach is probably more quantitative and repeatable, which is something we all want to be. Each circle is 0.5 miles in diameter.


Eastern shore of the northern end of Great Salt Lake, UT. I was hoping that the reddish water along the lake shore would display a band of higher photosynthesis, but it didn't. The color is produced by the red algae Dunaliella salina and haloarchaea bacteria. Pigments in these microbes absorb blue light (although they don't really do much photosynthesis) so I thought NDVI might be higher there. But the effect is too subtle to see easily.


White Mountain North, WY. Snow in the high country dramatically defined the topography of this ridge in southwestern Wyoming. The highest peak is about 7600 feet asl. I was pleased to see that snow has a very low NDVI value.


Contour farming 90 miles northwest of Chicago near Juda, WI. I didn't think I would be able to find this in Google Earth, but the base imagery is from just five weeks ago, so it looks exactly the same except that they have harvested some corn since then. In the NDVI image, the red strips and patches (highest NDVI) are hay or other green crop, and the yellow or green strips or patches are corn which has tasseled and browned and is ready for harvest or has already been harvested.

. Previous Mentor Summit notes


I love these, Chris. makes me want to process some of my passenger-pigeon shots.

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