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It's functionally equivalent to an RTK base station (the configuration script I'm using is even called "RTKbase"[0]), but it's being used for researching GPS-based soil moisture retrieval[1]. Basically the GPS signal bounces off the ground and causes an interference pattern that changes based on the wetness of the soil.

There is actually a permanent survey grade GNSS reciever about 200 m away from the u-blox receiver. But the geography around it (too hilly) means it doesn't work for soil moisture retrieval.

[0] https://github.com/Stefal/rtkbase/ [1] https://gnssrefl.readthedocs.io/en/latest/pages/understand.h...

I'm running a Raspberry Pi based GNSS receiver from a 26 Ah SLA battery and an 80W panel. Just passed 2 weeks of uptime in a cloudy period of southern hemisphere autumn.

A monte carlo simulation using historical conditions said it had a ~95% chance of no downtime over 3 winter months. A slightly larger battery would bring that up to 99%.

The Pi (3b+), GNSS reciever (u-blox ZED F9P), and Waveshare 7600G 4G modem average about 3.5W idle. The GNSS reciever is about 0.1 - 0.2 W of that. Wifi would be more energy efficient, I imagine.

To expand upon this:

>> They're measuring it by looking for phase differences in the received L-band (~2GHz) signals

The "L-Band signals" are GNSS signals, for example GPS L1 and L2, which use a carrier wavelength of 1575.42 MHz and 1227.6 MHz, respectively. Both L1 and L2 signals are emitted at the same time, but experience differing levels of delay in the ionosphere during their journey to the receiver. The delay is a function of total electron content (TEC) in the ionosphere and the frequency of the carrier wavelength. Since we already know precisely how carrier frequency affects the ionospheric delay, comparing the delay between L1 and L2 signals allows us to calculate the TEC along the signal path.

Another way to think of it is: we have an equation for signal path delay with two unknowns (TEC, freq). Except, it is only one unknown (TEC). Use two signals to solve simultaneously for this unknown. Use additional signals (like L5) to reduce your error and check your variance.

Is paid software OK? Have you looked at Revit?

This comment made me curious.

Apparently, TAI specifically defines the second (in terms of cesium transitions) at sea level (where gravitational potential is equal). I never knew that second part.

If you want to go further down the LIDAR path, you might be able to improve the public data by making manual improvements to the point cloud classification.

For that sort of terrain it's common for classification algorithms to put vegetation (e.g. deadfall, small bushes) into the "ground" class, so when the terrain model gets triangulated using all the "ground" points there is erroneous bumps. If this is the case, you could reprocess the point cloud yourself and tweak the settings being used or make manual adjustments.

I'm not sure of the quality of the linked dataset, so maybe it would be difficult to find improvements. But you knowledge of on-the-ground conditions (and smallish scale of the area) means it's definitely possible.

Also, just in case you haven't stumbled across it, a "Digital Surface Model" (DSM) is different than a "Digital Terrain Model" (DTM)!

(surveying student here, very much enjoyed the writeup!)

More specifically, you need to solve for the receiver clock bias.

https://www.e-education.psu.edu/geog862/node/1724

Edit: I would welcome corrections though if I am misunderstanding. Perhaps if you're not interested in precise timing you can read the satellite time from the broadcast signal?

Edit 2: OK, I think I understand your point now. The satellites broadcast their timestamps directly. To find a precise position / time you need to find a correction to the receiver clock. But if you don't need a very precise time, you can just use the satellite timestamp.

GPS determines a solution for position and time simultaneously. It requires 4 satellites to solve for 4 unknowns (X, Y, Z, t). If you know your position you can solve for time using only 1 satellite, but a watch is always moving so it's position won't be known.

A group of students at my university were claiming their papers were being marked by a LLM. They cited a classifier like the OP which they used on their feedback comments.

I'd also be interested in further discussion into something like that. Talk about deja vu.

A friend of mine once described this as a "critical hit chance" (ala video games). There's not much chance of a 'critical hit' if you're just hanging around home, for example. But if you're on the road, stopping in at a random pub for dinner? There's that chance something special happens.

Sometimes it might be better to trade the option with higher average damage for one that is more volatile, because you might get lucky at just the right moment.

> What the US government did was remove the bias from the CA code so it could be used for precise positioning. The military still uses P codes as well. I believe there is a small gain to be had but it’s due to frequencies.

The precision of positioning from the P code is 10 times greater than the C/A code (about 30cm vs 3m). This is due to the wavelength/'chip length' of the code signal which is modulated onto the carrier wave (10.23 Mhz / 29.31 m wavelength for P code, 1.023 Mhz / 293.1 m wavelength for C/A code). Positioning precision is limited to about ~1% of the chip length by signal processing.

I'm quite early in the course, so couldn't give you a good answer sadly.

The intro to surveying class had a very broad overview of the history- important technologies, discoveries, and figures.

There is a Surveying and Engineering Law class that I expect will contain a lot of historical cases. Otherwise, there are no specific classes, so any history will probably be dispersed throughout the degree.

I'm a first year Surveying student, after I spent all of high school thinking I'd study computer science / software. I don't see much discussion of the topic on HN so I'm glad this is getting upvoted!

The opportunity of working outdoors appeals to me a lot, as does the technology (drones, remote sensing, GIS). It also seems like a much more relaxed job market than a more traditional tech / engineering job (albiet with less pay).

I'd love to hear any thoughts on the profession or suggestions for those early in their career.

Tweet from Tjukanovt: https://twitter.com/tjukanov/status/1443868144905428992

I use Ripcord[0] on my desktop/laptop, a Discord client which provides easy switching between accounts. It's lightweight and supports slack, too.

[0] https://cancel.fm/ripcord/

I've heard a similar story about an experiment with monkeys, apparently called the 'five monkeys experiment' [1].

A group of monkeys were put in a room with a ladder leading to a banana. When a monkey touches the banana, sprinklers turn on and soak the room. The monkeys quickly learnt to ignore the banana to avoid getting wet, and even physically stopped newly introduced monkeys (who were unaware of the sprinklers) from climbing the ladder.

The entire group was eventually replaced one by one. The replacement group had never seen the consequence of climbing the ladder, but policed eachother as well as any new members from eating the banana.

[1] https://workingoutloud.com/blog/the-five-monkeys-experiment-...

> Of course, I'm not even sure how many modern/younger readers will understand why "^H". I'm getting too old for this.

For all the other modern readers: http://answers.google.com/answers/threadview/id/386870.html