3 ms·

Stupid question. I was under the impression that one of the limits of 5g was that it was a short-distance signal, easily blocked by a wall or any obstacle. Is i

by cm2187 8y ago

Stupid question. I was under the impression that one of the limits of 5g was that it was a short-distance signal, easily blocked by a wall or any obstacle. Is it really going to create interferences all the way to space? I thought satellites measured the temperature of the top of the atmosphere, not of stuff on the ground.

lgeorget 8y ago
They actually measure a lot of parameters, not only temperatures, and in all the layers of the atmosphere. And they're _very_ sensitive. For some forecast needs (short term forecast, storms, etc.), the conditions under the atmospheric boundary layer (https://en.wikipedia.org/wiki/Planetary_boundary_layer https://en.wikipedia.org/wiki/Planetary_boundary_layer) is what matters most, so the microwave noise near the ground is definitely an issue.
pas 8y ago
Typical signal transmission uses a a signal to noise floor of something like 20-40 dB ( https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Signal-to-Noise_Ratio_(SNR)_and_Wireless_Signal_Strength https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Pra... ) for high speed data transmission, but if you want to just get a big fat one or zero across, then you don't need that much. And antennas are really good at picking up resonant EM radiation, even if it's not the "full signal". But these very sensitive weather sensors. And they already work by detecting a trend and then detecting a big blip over that. (So rain currently looks like some sort of interesting blip in the noise.) So, it might be possible to have cities mapped with a differing trend, but it would further complicate models. And currently over land there's not much noise, because humans don't use this part of the EM spectrum. Mostly because it's not great at long range, because attenuates very fast exactly due to water vapor in the air. So it was "easy" to exploit this for getting weather data, because it was reasonable to assume close to constant natural emissions. (Probably only a simple daily and seasonal trend. Though it might be already necessary to handle differences between woodlands and urban areas.) (See also, why it's hard to do the same over water: https://www.researchgate.net/publication/252663726_The_Effect_of_Signal-to-Noise_Ratio_on_the_Study_of_Sea_Level_Trends https://www.researchgate.net/publication/252663726_The_Effec... )

by cm2187 8y ago

lgeorget 8y ago

They actually measure a lot of parameters, not only temperatures, and in all the layers of the atmosphere. And they're _very_ sensitive. For some forecast needs (short term forecast, storms, etc.), the conditions under the atmospheric boundary layer (https://en.wikipedia.org/wiki/Planetary_boundary_layer https://en.wikipedia.org/wiki/Planetary_boundary_layer) is what matters most, so the microwave noise near the ground is definitely an issue.

pas 8y ago

Typical signal transmission uses a a signal to noise floor of something like 20-40 dB ( https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Signal-to-Noise_Ratio_(SNR)_and_Wireless_Signal_Strength https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Pra... ) for high speed data transmission, but if you want to just get a big fat one or zero across, then you don't need that much. And antennas are really good at picking up resonant EM radiation, even if it's not the "full signal". But these very sensitive weather sensors. And they already work by detecting a trend and then detecting a big blip over that. (So rain currently looks like some sort of interesting blip in the noise.) So, it might be possible to have cities mapped with a differing trend, but it would further complicate models. And currently over land there's not much noise, because humans don't use this part of the EM spectrum. Mostly because it's not great at long range, because attenuates very fast exactly due to water vapor in the air. So it was "easy" to exploit this for getting weather data, because it was reasonable to assume close to constant natural emissions. (Probably only a simple daily and seasonal trend. Though it might be already necessary to handle differences between woodlands and urban areas.) (See also, why it's hard to do the same over water: https://www.researchgate.net/publication/252663726_The_Effect_of_Signal-to-Noise_Ratio_on_the_Study_of_Sea_Level_Trends https://www.researchgate.net/publication/252663726_The_Effec... )