Made a quick trip to Greenland for three days in July to work on some equipment there. I did not get on the air due to work activities and operation of the incoherent scatter radar whose modulator trashes the HF bands if you’re close to it (i.e., same building). A few photos, though. These were all shot with an iPhone 5s, nothing fancy.
Posts Tagged ‘science’
“One man’s signal is another man’s noise,” began Dr. Kudeki as he derived incoherent scatter radar theory from Nyquist’s noise theorem in ECE458. I think of that statement often, whether it be QRM on the ham bands or sifting through the pocket litter of web users looking for their consumption preferences.
This morning, I admired just such an example of signal and noise while watching the NOAA Doppler weather radar. Undesired targets of a radar that return echoes are termed “clutter” in the radar parlance and one simplistic way of eliminating clutter, especially when you expect the desired scatterers (“targets”) to move, is to assume that all of the stationary returns are clutter. In the weather radar, we get clutter from all sorts of stationary things like trees, hills, and buildings. Of course, what causes the clutter to move?
You see, it was one of those humid August mornings when a ham’s mind wanders to…tropospheric ducting. Yes, indeed the clutter returns were moving, intensifying before and after sunrise. I was fixated on this and watched the loop over and over again before noticing an even more interesting bit of clutter!
Beginning at 0958 UT on 4 August 2014, there is a small ring forming out over the Elk River area. The ring, which is indicated by the downward-pointing vertical arrows, expanded over the next >40 minutes. I was puzzled and watched the loop over and over. I considered and discarded a number of theories before resorting to Google. Apparently, it’s very likely a flock of birds. Sure enough, the epicenter of the ring is Elk Neck State Park. Fascinating.
The slanted arrows in the figure above indicates the ground clutter that I was originally noticing as a signature of tropo ducting, obviously now of secondary interest in this sequence of images!
Epilogue: I sent these frames to my father, who is an avid observer of the natural world. He passed them along to two friends back home who are birders. At press time, one reported that he had learned of these “bird circles” from Greg Miller, another birder from the area who got famous as one of the subjects of the book (and movie of the same title) The Big Year. I haven’t read/seen it, but I guess they went to Adak, which has a special place in my heart. Anyhow, it’s a funny small and interesting world in which we live.
I was enjoying a leisurely sweltering summer Sunday afternoon in the back yard with Evan, Sarah, two Adirondack chairs, a kiddie pool, and the schematics for an IC-290A I have on the bench. I came in to get a glass of water and while I was inside, I checked my e-mail (since I have some equipment for sale). No prospective buyers, but I did have a message from Sean, KX9X, that he was working aurora on 6 and 2 meters. I quickly plugged in the 2-meter rig and swung the beam around to the north. Sure enough, there were raspy aurora signals all over two meters. I quickly put N9GX (EN60) in the log for my first ever aurora QSO. This was at least as cool as working K5QE on 2-meter Es with 10 watts.
So, I fumbled around a drawer and pulled out a cable to connect the TS-700S to the computer and fired up Audacity. I made this interesting recording of KA1ZE/3. I started out with the beam to the NE (45 degrees azimuth) with a strong auroral buzz on Stan’s signal. Then I swung the beam around to the NNW direct path (345 degrees azimuth). I’m in FM19la and he’s in FN01xt, which is exactly 200 miles (322 km) direct path. On the direct (forward tropo scatter) path, there is still a hint of aurora, but the tone is a bit purer. When I turn the rotor there is pretty bad hum from a (not unexpected) ground loop.
In order to better visualize a few things, I ran a short-time Fourier transform (this is the actual technical term for a “waterfall”) on the audio file. I need to code-up a polyphase implementation of the FFT like that used in Rocky, but there are only so many hours in a day. Click on the image for full-size.
There are lots of interesting details here. First, you can see that the auroral scatter is both Doppler-shifted (lower in frequency) and Doppler-broadened (spread out from the central frequency) compared with the direct tropo scatter signal. Second, you can see the ground-loop-induced hum at the low-frequency end. Auroral backscatter comes from field-aligned plasma density irregularities embedded in the auroral convection flow. Because most readers will be allergic to the vector math, we make the (somewhat gross) approximation that KA1ZE and I are transmitting and receiving from the same location. Now, we can take a stab at estimating the flow velocity from the following equation:
Where delta-f is the Doppler shifted frequency (about 300-Hz from these data), c0 is the speed of light (300,000,000 m/s), f is the carrier frequency (144 MHz), and vflow is the flow velocity. While we’re making approximations, if we round f up to 150 MHz, the twos cancel and we get the Doppler shift of 300 Hz corresponding to a flow velocity of 300 m/s (670 mi/hr). Fast! Because it is lower in frequency than the direct signal, we can also infer that the flow was directed away from us.
There you have it! Science fair projects with your ham radio.
Last year, I managed to scrape together some equipment funds at work to buy a small spectrograph system for studying atmospheric light emissions (airglow and aurora). A co-worker secured the funds and contacts for us to install it at an observatory in Greenland. Because we need to make the measurements at night, and because the instrument was delivered in early December, we made immediate plans to go to Greenland as soon as possible. (Sarah is certainly laughing at this point because the plans were actually far from immediate and we bought our passage just over one week before departure.)
Greenland is only a short (4- to 6-hour) flight from the NE U.S., however the only route that operates in winter (and indeed the only commercial route) is on Air Greenland via Copenhagen, which operates four round-trip flights per week in winter. This turned getting there into a two-day affair of perverse travel arrangements totaling over 12,000 air miles to go about 4200 miles round-trip on the great circle. I met my co-worker, a United Airlines devotee (myself an American Airlines devotee), in Copenhagen and we flew to Kangerlussuaq (Sondrestrom) on Air Greenland.
One of the things that strikes you about Greenland as you approach Kangerlussuaq is how otherworldly and remote it is. Kangerlussuaq is the site of the former U.S. Sondrestrom Air Force Base, and one of two runways (the other is at Thule) on the island large enough to accommodate aircraft capable of flying to Greenland from abroad (this is a mild, although amusing exaggeration). Air Greenland has its hub there, shuttling passengers off to towns around Greenland on twin-engine turboprops like the Dash-8. It is, as our host explained, “…not your typical Greenland town. It is far inland at the end of the fjord and not on the coast. The only reason it exists is because of the airport.” Fuel and supplies are all brought in from outside. Like most current and former U.S. military installations worldwide, it is reliant on diesel fuel for its on-going existence. It’s sobering to be someplace that is totally unsustainable, although one might argue similarly of many U.S. cities, but I digress.
Kangerlussuaq is also near “the dog line,” north of which sled dogs are very common. Here is one of the two road hazard signs we saw while driving around…dogsled crossing:
The instrument set up easily the first afternoon and we were able to collect some data with it that night. As we were setting the instrument up, we heard reports of an Earth-directed CME from the Sun and hoped for aurora over the next few days. We were not disappointed…
The second night, I stood “aurora watch” in the cold while my warm-blooded co-worker processed the previous night’s data. Soon, I saw some faint cloudy white sheets way down on the horizon and I ran back in to alert him and retrieve the camera tripod. This photograph was taken facing toward the east southeast.
And, the 3.5-MW peak L-band incoherent scatter radar was running. The dish is blurred because it is moving.
And, here is a shot of my fan dipole strung up on the DK9SQ mast.
Speaking of radio, I did manage to make a few QSOs as OX/K8GU on 17 meters, but not as many as I would have liked. The combination of high absorption in the auroral oval (mostly to our south during our stay), little sunlight, a poor low-angle shot (required to avoid the auroral zone) to North America, short openings, and the fact that we were well-occupied with work for the four days we were there conspired to keep my contact count low. QSOs will go into LoTW soon—the certificate was issued yesterday. I have not yet designed a card, but there will be a special card. Thanks to those who did contact me.
Teaching Evan the basics of radar signal processing with this baby-block 7-bit Barker code and its matched filter.
A few photographs from work on the Wallops Island SuperDARN radar last week…
Slate Labs has an “interactive tool” to look at food deserts in the U.S. by county—places where a healthy variety of food is unavailable. They define a metric of desertification by counting the number of people who do not have access (not sure how this is defined) to a car AND live farther than one mile from a supermarket (not sure how this is defined, either). So, I went looking at some places I’ve lived.
My home county is Holmes County, Ohio. If you look at the map, it’s the one that’s an island of dark brown in the middle of Ohio. 27.91 percent of Holmes County is a food desert by this metric! Blame it on the Amish. Because the county is rural, there are few grocery stores. And, because the Amish do not have access to their own cars, they count a large portion of this population. Other counties with large Amish populations (relative to the non-Amish population) also stand out clearly.
It also appears that the map is distorted by population density, with sparsely populated areas being more prone to classification as food deserts. Is this fair? Is there anything that can be reasonably done about these areas even if they are food deserts? I don’t at all disagree that this is an important, significant problem, but it seems that there might have been a better metric. Perhaps it’s the most accessible metric with the available data?
Although this map may be revealing in many ways, it also distorts the reality a bit. For me, it’s a reminder to not consume “news infographics” too casually. I haven’t read all of the comments on the Slate piece and probably won’t. So, forgive me if someone has already noted some of the above. As a final note, most of the people who write for Slate are relatively ignorant of what happens in the part of the country between the Coast Ranges and the Appalachians. So, as one commenter wrote, it’s a “typical urbanite view” of food.