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33 votes
Accepted

What is this "crystal ball" located at a meteorological station?

It's a Campbell-Stokes sunshine recorder, used to record the times at which the sun is shining. It acts as a lens, focusing the sunlight onto a piece of card. If the sun is shining, the focused beam ...
Pont's user avatar
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17 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

Mark's answer about mercury barometers is correct - but it is not the complete story. Barometers were initially constructed using water, not mercury, on the manometer principle. Water is lighter ...
Graham's user avatar
  • 437
17 votes

Ways to make a "How hard is it raining?" detector for personal use?

If you're open to a more mechanical solution, I'd suggest building a "tipping bucket rain gauge", best explained by a picture (source: https://www.researchgate.net/figure/Sideview-of-tipping-...
Max Klein's user avatar
  • 271
14 votes

Ways to make a "How hard is it raining?" detector for personal use?

Upon reading the question my first thought was, please define what is meant by "how hard is it raining?". My initial tangent thought was "what about the impact energy of the rain" -...
Fred's user avatar
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13 votes

Ways to make a "How hard is it raining?" detector for personal use?

One way to do that is to estimate how much water is changing. If you can ignore the spill over, then that is approximately how much the puddle is changing. Another idea you can use is to measure the ...
BarocliniCplusplus's user avatar
13 votes

Ways to make a "How hard is it raining?" detector for personal use?

It's not perfect, but a simple solution to the issue of a puddle building up on the resistance plate is to tilt the plate a bit, so that instead of the water building up on the plate it runs off. Your ...
C_Elegans's user avatar
  • 231
9 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

A mercury barometer is a simple, easy-to-build barometer that turns the problem of calibrating a pressure standard into one of calibrating a length standard. Accuracy of length standards has long ...
Mark's user avatar
  • 1,261
9 votes

What are these Gizmos at Izaña Atmospheric Research Center in Spain?

Those are Sun/Moon multispectral photometers and ski radiometers. These are instruments that can scan the sky or track the Sun/Moon for direct measurements. They measure light intensity at multiple ...
Camilo Rada's user avatar
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9 votes

Are there any DIY conductivity sensors that will hold calibration for long periods? {multiple months}

I've built DIY conductivity probes for subglacial measurements. Unfortunately my sensors remain under ~100m of ice so I haven't be able to recover them to check the calibration, but for the same ...
Camilo Rada's user avatar
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8 votes

Why are CO2 sensors so expensive when CO sensors aren't?

Carbon monoxide (CO), natural gas & hydrocarbons, VOCs, ammonia, etc. In this Chemistry SE answer and this Electronics SE question I discuss how the family of MOS gas sensors work. They can ...
uhoh's user avatar
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7 votes

How is relative humidity determined from a wet and dry bulb readings?

Edit: 1 May 2021 The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer. The procedure is a ...
Fred's user avatar
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7 votes
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Using accelerometer as a seismograph

The magnitude of an earthquake is related to the total energy released, therefore to estimate it from a seismogram you need to know the distance to the source. In the case of the Richter scale for ...
Camilo Rada's user avatar
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6 votes
Accepted

What is this upside-down transparent funnel-shaped item on a weather monitoring station?

The upside down funnel-shaped attachment is used to prevent rain-water getting inside the inlet of instruments which analyse ambient air. Usually, these instruments are air pollution monitoring ...
Harish's user avatar
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6 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

I don't think they are using that level of accuracy for the old readings. Reporting pressure, in hPa, to one decimal place is being done for recent measurements. There are no values given for very ...
Fred's user avatar
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6 votes

Ways to make a "How hard is it raining?" detector for personal use?

I would approach this by counting pings on a plate with an attached piezo or microphone. The amplitude of the ping will give the volume of the drop and the number of pings the drop quantity. This is a ...
user2825367's user avatar
6 votes

Ways to make a "How hard is it raining?" detector for personal use?

A 'video disdrometer' is a device for characterizing raindrop size distributions. Professional versions (e.g A 1D distrometer) can use a video camera to image the shadow cast by water droplets moving ...
Andy M's user avatar
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6 votes

How did they know that there was a "desert tsunami" in a Death Valley cave after a 7.6 magnitude earthquake near the southwest of Mexico?

The news section of the Death Valley National Park website has the story: Mexican earthquake sloshes Devils Hole. There is footage of the waves at the end of the page. Here is a screenshot from the ...
Jean-Marie Prival's user avatar
5 votes

What does a floating mercury barometer look like? How does it work and how is buoyancy used?

A good place to start would be with Fortin barometers. They were "commonly used at meteorological stations to measure atmospheric pressure". The advantages of this type of barometer are its ...
Fred's user avatar
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5 votes
Accepted

Which particles are classified as PM2.5? How exactly is this defined?

I think answering your questions in reverse will make more sense. The "size" of PM is typically the aerodynamic/inertial impaction size, as you guessed. My standard reference for this is this paper. ...
Jareth Holt's user avatar
  • 1,381
4 votes
Accepted

Which type of seismic sensors usually used in Earthquake Early Warning?

Accelerometers, preferably triaxial (i.e., those that record horizontal and vertical motion). Beyond that your question is indeed a bit too open-ended. Some use many cheap MEMS (http://onlinelibrary....
Erik's user avatar
  • 1,999
4 votes

Ways to make a "How hard is it raining?" detector for personal use?

I sort of accidentally did this in one of my projects in a complicated, backhanded sort of way. I installed 16 soil moisture sensors in my yard as part of an attempt to track the distribution of water ...
JRE's user avatar
  • 141
4 votes

How do meteorologists accurately measure outdoor air temperature? There's sunlight, local trapping of air, radiant heat, precipitation

True air temperature may be an elusive quantity to measure but shielding thermometers and sensors from direct solar radiation has been the main approach for a long time. The best results are provided ...
Peter Jansson's user avatar
3 votes

Why are CO2 sensors so expensive when CO sensors aren't?

I think the core of the answer should lie in what was already stated in the comments. These detectors are not scientific instruments. For air quality monitoring much more sophisticated analyzers are ...
Janina's user avatar
  • 265
3 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy? To compare records of barometric temperature, this standard doesn't necessarily have to be met. ...
Will's user avatar
  • 131
3 votes

How does a whirling hygrometer work, how does it differ from static dry/wet bulb thermometer, and how to obtain humidity from its readings?

Instead of «whirling thermometer» you probably refer to «sling psychrometer» consisting of a dry-bulb thermometer and a wet-bulb thermometer. Yet, different to a static wet-bulb thermometer shown in ...
Buttonwood's user avatar
3 votes
Accepted

What is a Micro-Aethalometer; how do portable Black Carbon (BC) Monitors work?

Following @ Friddy's comment, I started reading Aethlabs AE51 FAQ and was quite surprised! While a conventional aethalometer use a long tape and move it to the new position after each measurement (...
uhoh's user avatar
  • 7,070
3 votes

Atmospheric visibility measuring device

The transmissometer setup should be quite easy to build in principle, but it could be hard to get accurate values. I did a very similar instrument but to measure water transsmisivity (a.k.a. turbidity)...
Camilo Rada's user avatar
  • 17.7k

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