Making NOAA's MMTS wireless

This is a custom wireless MMTS with internal data logger that I built, view from my backyard.

NOTE: yes I know it is not the best placement, this is just a preliminary test.

Those who have followed my work surveying official climate stations and their placement issues also know that I’ve been critical of the MMTS (Max Min Temperature System) which has been deployed at a majority of the COOP and USHCN networks. As of this writing, 55% of USHCN is made up of the original MMTS system, with 16% of the network being the improved “Nimbus” version, which has a display unit with max-min memory to prevent data loss. With 71% of the USHCN network being based on MMTS technology, it represents the major component of surface temperature measurement.

The big problem with MMTS is the fact that it is a cabled sensor, whereas the original Stevenson Screens could be placed anywhere, and often at better locations, the MMTS system cable often prevented proper placement because NWS COOP managers could not easily run the cable under walkways or driveways, since they lacked heavy equipment and time. This despite the fact that the original specification for MMTS cabling allowed for distances up to 1/4 mile. Stated simply; COOP managers don’t have access to trenching machines, and installation work is often done with shovels in a single day. 

So, I decided to solve the problem.

The cabling problem has routinely placed MMTS sensors closer to the residences and offices of COOP observers, which has resulted in most USHCN stations that have MMTS/Nimbus being rated a CRN4 due to building/asphalt/concrete proximity of 10 meters or less.

The USHCN station at Bainbridge, Georgia surveyed by Joel McDade is a perfect example that illustrates how an obstacle like a road prevented placing the MMTS unit at the previous location where the Stevenson Screen used to be. Hence, the measurement environment is now entangled with shade tree, asphalt, air conditioner, and nearby building issues.

Bainbridge, GA USHCN station, MMTS in foreground, Stevenson Screen in background

The solution is a wireless MMTS, and that idea has been bandied about by NOAA, but never implemented.

From the NWS San Diego website http://www.wrh.noaa.gov/sgx/cpm/temperature.php?wfo=sgx

“Currently, the MMTS requires a cable to connect the sensor with a display. Future plans are for wireless displays. This would eliminate many of the problems associated with cabled systems.”

I’m pleased to say that I have constructed and am now testing a prototype wireless MMTS unit as shown in the photo at the top of this post.

This unit departs from typical design in that is is entirely self contained, running on a small battery, and logs not only temperature, but humidity and dewpoint data also. Connection is via a USB port, and the data can be downloaded into a PC in comma delimited format, ready to graph or to upload to a central data collection point. The unit is a combination of some off the shelf parts, some hardware that I’ve added, and some modifications for the purpose of climate observation. The Gill shield (IR shield) is of my own design, but the datalogger unit could easily be installed inside most any existing NWS MMTS shield, or commercially available Gill shield. I’m working directly with a company that has created the basic battery powered microcontroller design to make it work in this climate monitoring application.

The beauty of this system is that it can be left running for days, weeks, and even months (depending on logging interval) and then the data can be downloaded in the field to a laptop. This allows for placement of these units at locations for use in studies of UHI, and cross checking of existing USHCN locations. The datalogger is programmable in many ways and can be adapted for various monitoring tasks.

Here is what the internal sensor package/datalogger unit looks like:

The  sensor package/datalogger unit simply inserts into the center fitting of the Gill shield, and the entire assembly simply screws onto the pipe fitting on the mounting pole. To get the data, simply unscrew the Gill shield, place it on a surface, plug in a USB extension cable, and download the data. A waterproof USB port could also be installed on the side of the pole to allow field connections without dis-assembly.

The entire sensor package/datalogger and Gill Shield w/pole unit was created for less than $150 in parts. I expect costs will be much lower as production costs are tuned.

Now there’s no reason to compromise placement, or fret over trenching cables.

Here is a list of features and specs:

• Temperature in Centigrade or Fahrenheit, programmable
• Range of -35° to +80°C (-31 to +176°F)
• Dew Point in Centigrade or Fahrenheit, programmable 
• Humidity in 0-100 %RH
• Data logging intervals from 10 seconds to 1 hour
• Internal data memory from days to months, depending on logging interval
• Battery life up to one year
• Inexpensive and portable
• Resolution of 0.5 degree
• Status LED’s indicate operation and fault conditions
• Operates on a single 1/2 size AA 3.6V Lithium Battery

Specifications

I’m working on improving the accuracy of the sensor, and I’m investigating an NIST calibration process.

With the unit shown above in my yard, I’ll run a one week test to see how well it compares to my Davis weather station, and I’ll publish the results next week.

Here is a graph of a simple outdoor/indoor test I ran last night and today:

If there is interest, I’ll make these units available to anyone whom wishes to conduct experiments or to install and compare against nearby NOAA stations. if so, please advise me.