4 ms·

Speaking of anomalous geology, I went down a bit of a rabbit hole this evening, I was reading about survey grade compasses, and they are balanced to account for

by somat 3y ago

Speaking of anomalous geology, I went down a bit of a rabbit hole this evening, I was reading about survey grade compasses, and they are balanced to account for magnetic dip, the closer you get to the poles the more dip you have. And the manufacturer helpfully provided a map to help you pick the best dip correction. Looking at the credited source(the world magnetic model) for a bit greater resolution... And, what the heck is that in the south Atlantic ocean. https://www.ncei.noaa.gov/sites/default/files/2022-02/Miller%20Projection%20Main%20Field%20Inclination%20%28I%29.pdf https://www.ncei.noaa.gov/sites/default/files/2022-02/Miller... I think it is this, There is a large(very large) density structure in the mantle in that general area and it appears to drive weak van allen fields in the south atlantic. https://en.wikipedia.org/wiki/South_Atlantic_Anomaly https://en.wikipedia.org/wiki/South_Atlantic_Anomaly

grugagag 3y ago
I’ve heard of it but wasn’t aware it’s that ‘anomalous’. It looks like it would make a compass in the area very hard to use
- throwway120385 3y ago
  Only if you're traveling fast relative to walking speed. You can still generally navigate by direction in the area, and it looks like it covers such a large area that in EG a 5 mile by 5 mile area you could still reliably set your declination and navigate with minimal error. The field lines seem to change direction in an arc the size of South Africa, for example. But it just means that if you're westerly or easterly in South Africa you need to be very cautious to set the declination on your compass and not assume it varies little, like you can in the Pacific Northwest.
MPSimmons 3y ago
Spacecraft going through the SAA experience dramatically higher radiation hits.
hydrogen7800 3y ago
> I was reading about survey grade compasses, and they are balanced to account for magnetic dip, the closer you get to the poles the more dip you have. Wet, or whiskey compasses used in aircraft are counterweighted to account for this. There are mnemonics for pilots to know how to handle the error induced by this counterweight: "OSUN—overshoot south, undershoot north" and "ANDS—accelerate north, decelerate south". https://www.aopa.org/news-and-media/all-news/2012/may/flight-training-magazine/technique--compass-error https://www.aopa.org/news-and-media/all-news/2012/may/flight...
- psunavy03 3y ago
  And generally if you're using the whiskey compass, something is wrong, because most aircraft besides the most basic of VFR bugsmashers have other devices as a primary heading reference, be it a simple gyrocompass on a Cessna 172 or a full GPS-enabled strapdown inertial navigation system on a jet aircraft.
westurner 3y ago
Existing gravimeter tech: "City-size seamount triple the height of world's tallest building discovered via gravitational anomalies" (2024) https://www.livescience.com/planet-earth/rivers-oceans/city-size-seamount-triple-the-height-of-worlds-tallest-building-discovered-via-gravitational-anomalies https://www.livescience.com/planet-earth/rivers-oceans/city-... "Kerr-enhanced optical spring for next-generation gravitational wave detectors" (2024) , and/or Tantalum; https://news.ycombinator.com/item?id=39957123 https://news.ycombinator.com/item?id=39957123

by somat 3y ago

grugagag 3y ago

I’ve heard of it but wasn’t aware it’s that ‘anomalous’. It looks like it would make a compass in the area very hard to use

throwway120385 3y ago
Only if you're traveling fast relative to walking speed. You can still generally navigate by direction in the area, and it looks like it covers such a large area that in EG a 5 mile by 5 mile area you could still reliably set your declination and navigate with minimal error. The field lines seem to change direction in an arc the size of South Africa, for example. But it just means that if you're westerly or easterly in South Africa you need to be very cautious to set the declination on your compass and not assume it varies little, like you can in the Pacific Northwest.

MPSimmons 3y ago

Spacecraft going through the SAA experience dramatically higher radiation hits.

hydrogen7800 3y ago

> I was reading about survey grade compasses, and they are balanced to account for magnetic dip, the closer you get to the poles the more dip you have. Wet, or whiskey compasses used in aircraft are counterweighted to account for this. There are mnemonics for pilots to know how to handle the error induced by this counterweight: "OSUN—overshoot south, undershoot north" and "ANDS—accelerate north, decelerate south". https://www.aopa.org/news-and-media/all-news/2012/may/flight-training-magazine/technique--compass-error https://www.aopa.org/news-and-media/all-news/2012/may/flight...

psunavy03 3y ago
And generally if you're using the whiskey compass, something is wrong, because most aircraft besides the most basic of VFR bugsmashers have other devices as a primary heading reference, be it a simple gyrocompass on a Cessna 172 or a full GPS-enabled strapdown inertial navigation system on a jet aircraft.

westurner 3y ago

Existing gravimeter tech: "City-size seamount triple the height of world's tallest building discovered via gravitational anomalies" (2024) https://www.livescience.com/planet-earth/rivers-oceans/city-size-seamount-triple-the-height-of-worlds-tallest-building-discovered-via-gravitational-anomalies https://www.livescience.com/planet-earth/rivers-oceans/city-... "Kerr-enhanced optical spring for next-generation gravitational wave detectors" (2024) , and/or Tantalum; https://news.ycombinator.com/item?id=39957123 https://news.ycombinator.com/item?id=39957123