Rain sensor
Provided herein is technology relating to measuring weather data and particularly, but not exclusively, to apparatuses, methods, and systems for sensing hydrometeors (e.g., rain) and measuring hydrometeor characteristics (e.g., volume, rate, size distribution, etc.).
1. A sensing apparatus comprising:
a) a hollow sonde that is spherical with a center and an internal surface;
b) a stalk extending into the hollow sonde;
c) a transducer mounted on the stalk; wherein the transducer is spaced from the internal surface and spaced from the center; and
d) a gas or non-solid phase positioned between the transducer and the internal surface.
2. The sensing apparatus of claim 1 wherein said hollow sonde is made of stainless steel.
3. The sensing apparatus of claim 1 wherein the hollow sonde has a diameter of from 100 to 500 mm.
4. The sensing apparatus of claim 1 wherein the hollow sonde has a thickness of 0.5 to 5 mm thick.
5. The sensing apparatus of claim 1 wherein the hollow sonde has a characteristic frequency of 6 to 10 kHz.
6. The sensing apparatus of claim 1 wherein the transducer is an electret, piezo, or condenser microphone.
7. The sensing apparatus of claim 1 wherein the transducer is placed approximately 20 to 80 mm away from the center of the hollow sonde.
8. The sensing apparatus of claim 1 wherein the transducer detects sound waves that propagate from the hollow sonde to the transducer through the gas or non-solid phase positioned inside the hollow sonde.
9. The sensing apparatus of claim 1 wherein the transducer is placed approximately 25 to 75 mm away from the center of the hollow sonde.
10. The sensing apparatus of claim 1 wherein the hollow sonde comprises a limited rain-sampling area.
11. The sensing apparatus of claim 1 further comprising a solar radiance sensor.
12. A method of determining a rain rate, the method comprising:
a) providing an apparatus according to claim 1 ;
b) acquiring a real-time acoustic signal of rain drops impacting the hollow sonde of said apparatus;
c) processing said real-time acoustic signal to produce acoustic power data or acoustic energy data; and
d) determining a rain rate from the acoustic power data or acoustic energy data.
13. The method of claim 12 wherein determining a rain rate from the acoustic power data or acoustic energy data comprises producing a statistical parameter from a distribution of acoustic power data or acoustic energy data.
14. The method of claim 12 wherein processing said real-time acoustic signal comprises sampling an analog voltage to produce a digital time varying signal.
15. The method of claim 12 wherein processing said real-time acoustic signal comprises demodulating an amplitude modulated signal.
16. The method of claim 12 wherein processing said real-time acoustic signal comprises applying an envelope to the digital time varying signal.
17. The method of claim 12 wherein processing said real-time acoustic signal comprises downsampling the digital time varying signal.
18. The method of claim 12 wherein determining a rain rate from the acoustic power data or acoustic energy data comprises using a correlation between the aggregate signal of multiple droplet strikes and rain rate.
19. The method of claim 12 wherein determining a rain rate from the acoustic power data or acoustic energy data comprises using a power function to correlate between the aggregate signal of multiple droplet strikes and rain rate.
20. The method of claim 12 further comprising normalizing the acoustic power data and/or acoustic energy data using a normalization constant based on the maximum microphone signal detected in a normal rain.
21. The method of claim 20 wherein said normal rain has a maximum drop size of approximately 4.0 mm or 5.0 mm.
22. The method of claim 12 further comprising correcting the acoustic power data and/or acoustic energy data for wind velocity.
23. A system comprising a plurality of sensing apparatus according to claim 1 .