Field Report 2015-12-08: The Logging Rain Gauges Work!

Trish & Fernanda inspecting units before retrieval

Trish & Fernanda inspecting units before retrieval

We managed to squeeze in a short  fieldwork trip before the end of the year, and the growing number of loggers at Rio Secreto put that cave at the top of our list to give me enough time to service all the units.  It was also important that we get everything back into place before they were swamped by tourists wanting to spend their holidays in the sun, rather than shoveling snow.

I was very happy to see that only one single machine suffered a sensor failure, and this was one the surface drip units that we had cooked under the tropical sun during a previous deployment.  Some of our early monitoring stations are finally passing that critical one-year mark, so we can start to think about seasonal patterns in records that display this kind of short term variability:

Typical Drip Sensor record 2015, Rio Secreto cave

Drip count /15 min,  Station 10, Far Pool Cluster

RainGauge

I had no idea spiders were so fond of  living in climate stations…

We also had a several sensors on the surface, and I was really curious to see the the data from this first field deployment of the new rain gauges, given that so many of our cave records showed strong discontinuity events like the one above.  Not only did I want to see the quantitative data, I also wanted to know if the bottom shroud prevented the internal temperatures from going into to the 60°C range (which damaged several earlier loggers…)

And…. success! And both rain gauges were within 5% of each other, despite accumulations of bird poop & leaf litter, and one unit suffering from a slow tilt of nearly 10 degrees as the palapa roof shifted underneath it. With conversion ratios from my back-yard calibration, we were able to translate the drip counts directly into rain fall:

Rainfall (cm/day) data from one of our first rain gauge prototypes at rio Secreto

Rainfall (cm/day) from one of our first rain gauge prototypes at Rio Secreto

Trish had her doubts about this record initially, with so much rainfall occurring in what was supposed to be the local ‘dry’ season.  But after searching through data from nearby government weather stations, and comparing our surface record to the break-through events I was seeing in the drip data, we slowly became convinced that it had, in fact, been one of the rainiest dry seasons in quite a while.  We also had a beautiful temp record that showed the new cowlings pulled peak temperatures (inside the loggers) down by almost 20°C:

Rain gauge internal Temp from RTC registers.

Rain Gauge, Internal Temp (°C) from the DS3231 RTC register.

Hopefully this means that the SD cards are back in the safe operating zone, which I know from past failures is nowhere near the 85°C that Sandisk claims.

So the new rain gauges are working properly, adding another piece of hydrology instrumentation to the Cave Pearl lineup.  I would love to say that the Masons Hygrometers delivered another great success, but the analysis is turning out to be somewhat more complicated as the 96-98% RH variations pulled my wet bulb depressions right into the bit depth limit of the DS18b20’s , so I will have to keep you in suspense for a while as I chew on those numbers…

Addendum 2016-03-16

Well serves me right for counting my chickens: Turns out that the drip sensor based rain gauges suffer from spurious counts due to wind noise. But I’ve been running these guys at their highest sensitivity settings, so hopefully I can dial that back to reduce the problem. We also had the gauges on a soft palapa roof, which no doubt contributed to the problem.

This entry was posted in Developing a Drip Sensor, Developing other sensors, Expedition Reports & Updates. Bookmark the permalink.

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