ATMS 360 Homework and Course Deliverables (return to main page)
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Assignment 9 Analog and Digital Pressure Sensors

Pressure measurements are very important in Atmospheric Science.

Preparation: Make an account with Tinker Cad. We will use this to learn how to work with microcontrollers, sensors, and electronics.

Getting Started: How to setup the pressure sensors and get data from them.

Summary Steps:
1. Set up a circuit and sketch to acquire data from the analog pressure sensor.
2. Add a circuit for the BME280 digital pressure, temperature, and relative humidity sensor.
3. Here's the Arduino set up for the BME280 sensor.

Here's a wiring schematic for the analog pressure sensor.
The 4 BME280 pins to use are highlighted in yellow. Here's a wiring schematic for both the analog pressure sensor and a digital pressure sensor (BME280 replaces the BME180).

Here's a sketch for the analog pressure sensor. Use it to test that the analog pressure sensor is working.
Here's a sketch for the BME280 digital pressure sensor. If needed, install the Adafruit BME280 library.
Here's the sketch to use for combining the output from both sensors once you have them both working separately. We will use them both at the same time.
Save the data with CoolTerm as comma separated values.
Write the time and date to the file with CoolTerm also for measurements over several days (here's how).
We will acquire data for a few days to compare the pressure sensors over a longer time as part of this lab.


Click on image for larger version.


Procedure for pressure sensor measurements.

Use CoolTerm to save data for the following measurements in parts A-D.
Note with Cool term you can start capture to text file before connecting to the Arduino, so you can capture the data information.

Evaluate sensor stability by doing measurements over several days.

A. We're ready to test the sensors for use in a weather station.
Set up the computer so it doesn't go to sleep.
Write the time and date to the file with CoolTerm also for measurements over several days (here's how).
Set CoolTerm to start recording data to a text file.
Connect CoolTerm to the Arduino so that it will stream measurements to the computer until recording data to text file is ended.

Calculate pressure averages in Excel for both the BME280 and the analog pressure sensors. Get a calibration factor for the analog pressure sensor=(Average BME280 Value)/(Average Analog Sensor Value).
Change the pressure calibration factor variable, in the sketch near the top, from 1.0 to the value you obtained. Upload your program to the Arduino.
Both pressure sensors should measure close to the same value after this.

Make a new column for calibrated ambient pressure. Apply the calibration factor to it.
Calibrated Analog Pressure = Measure Analog Pressure * (Average BME280 Value)/(Average Analog Sensor Value).
The Calibrated Analog Pressure will be used in all of the graphs.

Make a time series graph with time in minutes on the x axis, with pressure from both sensors on the first y axis, and temperature on the 2nd y axis.
Observe anything of interest, especially if temperature changes correlate with pressure changes. (1st graph).

HINTS ON GETTING DATA INTO EXCEL AND REMOVING BLANK ROWS:
1. Importing into Excel: Read in delimited text: Include delimiters "space" "Tab" and "Comma".
2. Get rid of the empty rows:
a) Click on the first column to select the entire column (click on the A. The whole column should be highlighted)
b) Home:Find & Select (it's on the far right):Go to special:Blanks:OK (This should select only the rows with nothing in them)
c) Home:Delete:Delete sheet rows (This should delete only the rows that had nothing in them)1. Importing into Excel: Read in delimited text: Include delimiters "space" "Tab" and "Comma".
 
Evaluate the precision and accuracy of the pressure sensors by their ability to measure small pressure changes.
Use CoolTerm to save data to a file for graphing with Excel.

B . Do measurements with 1 second time average, holding the sensor 1 meter below the table top for 10 seconds, then up 1 meter above the table top for 10 seconds. Repeat this cycle at least 4 times, with a single data file (each cycle does not need its own data file). Meter sticks are available. If you can't lift move it a full meter up or below the table, record approximately how high or low it can be moved. (2nd graph).
Time in miliseconds is x axis, y axis is pressure for both sensors.

 

Investigate the effect of averaging time on accuracy and precision.
Use CoolTerm to save data to a file for graphing with Excel.

C. Then modify the code to obtain 10 second time averages. Test by holding the sensor low for 100 seconds, and high for 100 seconds.
Repeat this cycle at least twice. (3rd graph).
Time in miliseconds is the x axis, y axis is pressure.


Topics to include in your report

Introduction:
Part of this lab is to compare pressure measurements from two sensors.
Briefly discuss what is meant by 'accuracy' and 'precision' in respect to measurements to start the conversation about sensor measurement comparisons. Helpful presentation for this discussion.

Methods:
How do these pressure sensors work? It is a good starting point to look at the data sheets for the analog sensor and for the digital sensor and other information on the pressure page. The Freescale MPX4115AP and BME280 use a piezoresistive strain gauge for sensing pressure. Freescale is an analog sensor so the Arduino is doing the analog to digital conversion, requiring a number of hookup wires and components on the breadboard and to Arduino. The BME280 is a digital sensor, so the analog to digital conversion is accomplished within the component itself. Arduino just asks the BME280 for measurement values, and I2C communcations is used for the communication between them. The BME280 also reports temperature and relative humidity and a calculated pressure altitude (altitude determined from a pressure measurement.)

Results:
Use the figures created from measurements described in the Procedure below to answer the following questions.
Looking at the data from Part A, what is an estimated uncertainty in the measurements with each sensor? Do the two pressure sensors measure the same pressure value within the specifications given in their data sheets?

Are the pressure sensors precise enough to show the pressure difference between when the sensors are held high and held low (about a 2 meter difference in height? Are the pressure differences accurate, that is, close to the estimated value of about 0.10 mb/meter?

Compare the fluctuations of the pressure data measured at 1 second intervals versus 10 second intervals. How does averaging time affect the sensor's uncertainty?

Note on the analog sensor: It seems the 10 bit analog to digital (a/d) converter of the Arduino would not be able to resolve a pressure difference of about 0.1 mb associated with 1 meter height difference. 1 bit change in the a/d counts corresponds to a voltage change of about 0.005 volts, and a pressure change of and about 1 mb pressure.
Dither helps: the voltage source for the Arduino is noisy enough to cause around 50 mv or so of noise so that the a/d counts fluctuate to a useful average.
The example sketch for pressure averages the measurements of the pressure sensor voltage and the voltage divider voltage about 1800 times for each measurement.
Use of the voltage divider for the power supply voltage measurement is necessary since the a/d range is 5 volts, and direct measurement might be at or over the measurement range.

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Assignment 8: Radar Meteorology Application

The goal is to develop skill in working with meteorological radar data.
This assignment works with precipitation and Doppler data from NEXRAD radar.
Practice giving presentations of meteorological data.
Become familiar with commonly used meteorological data.
This is a two part assignment that will be placed in a single powerpoint presentation:

Part 1: An in depth view of a radar, its location, and recent data from it.
Part 2: A case study demonstrating acquistion and interpretation of archived radar data for the same or another radar location.

Deliverables:
A. Presentation turned in through webCampus as a Powerpoint document. (50 points possible)
B. Deliver your presentation to the class. (50 points possible)


A note about time conversion. This site describes how to convert time in UTC to local time (scroll down to get specific instructions). For example, Reno is in the Pacific Standard Time (PST) Zone so that a local storm happening at 10:00 am PST corresponds to time UTC=PST+8 hours=18:00z. The 'z' is added to the time to indicate UTC.

Part 1: Introduction
Choose a radar. Here's where to choose the radar.
It's best to find a radar site that has active precipitation going on so that you can see data from it.
Find the coordinates of your radar for locations in the continental US (for Alaska, Hawaii, etc you'll need to estimate the coordinates).

Presentation Contents Part 1:
1. Put your radar coordinates into Google Earth and make an image of the location of the radar.
Using Google Earth, place circles centered on your image having a radius of 50 and 100 nautical miles, to represent the range of the radar and help interpret the images in parts 2 and 3.
2. Get a GIF movie of 24 images of base reflectivity data from your radar a day when precipitation is present.
Use the Save Data tab to make and save the GIF movie.
3. Get a base velocity 24 image GIF movie of base velocity for the same time.
Use the Save Data tab to make and save the GIF movie.
4. Get a correlation coefficient 24 image GIF movie of the base correlation coefficient for the same time.
Use the Save Data tab to make and save the GIF movie.

Discuss the location of your radar, in particular, any challenges that come about due to location.
Discuss the dbZ level of your base reflectivity GIF movie. Is it large or small, associated with rain and/or snow?
Discuss your base velocity GIF movie, interpreting wind direction and speed.
Discuss your correlation coefficient GIF movie, interpreting the values.

Part 2: Application
Find the time and location of a notorious weather event from anywhere in the continental US at a time when radar data is available. Be sure to note the local time and the 'Coordinated Universal Time' (UTC) time. Possibilities include tornados, hurricanes, derechos, severe thunderstorms, outflow boundary from convective storms, pyrocumulus clouds and/or fire tornados during wildland fires.

Email me the date, time, and location of the event you want to use.
I'll let you know right away if it is suitable and to make sure no one else is doing the same case study.

First, using the date and time in UTC for your event, go to the archived radar data page to be sure your location and time actually has an active storm. This is to make sure that you have the right day, time and location for your weather event, though including this this data in your presentation is optional.
Second, use the NOAA Weather and Climate Toolkit to get the data from the radar closest to your event; obtain animations over the event for reflectivity, radial velocity, and correlation coefficient.
Step by step instructions are given below under Resources for the NOAA Weather and Climate ToolKit (WCT) NEXRAD radar data and animation.

Presentation Contents Part 2:
5. Describe your notorious event.
6. Describe the radar location for your event as in Part 1.
7. Show the radar reflectivity movie for your notorious event and interpret it. Discuss any observational challenges that could have affected radar data, such as beam blocking, etc.
8. Show the radar Doppler velocity movie for your notorious event and interpret it.
9. Show the radar correlation coefficient movie for your notorious event and interpret it.
10.Show and discuss the HYSPLIT model 2-day-back-trajectory for air arriving at 100 meters above the Earth's surface (AGL) at the tornado, etc location. (Time zone discussion).

Discuss your notorious event and the data from it.

Resources for Software Tools
Install Google Earth, or use it with a browser.
Install Powerpoint or use it from a browser, or use Google Docs, or Pages on the Mac. Students can download Microsoft Office for free through Office 365.
It may be useful to also explore the National Weather Service radar site.
NOAA Weather and Climate Toolkit to obtain past data.

Resources for Radar Understanding:
Great discussion of radar and its applications. (local backup)
Radar discussion.
Interpretation of the radar correlation coefficient. (local backup).
National Weather Service discussion of radar, and another more in-depth discussion.
High windspeed problems with the nexrad radar due to aliasing. Equations and text backup.
Range folding in radar echos.

Resources for Notorious Weather Events:
Case study of a severe storm analyzed by radar.
Tornado discussion.
Tornados in the US since 1950, also given by year when you scroll down and click on a year link.
Strong hurricanes that have hit the US.


Detailed Resources for the NOAA Weather and Climate ToolKit (WCT) NEXRAD radar data and animation:
1. After downloading WCT, find the folder it's in and click on the file wct.ext.The first time it runs there will be a caution about the file. Go to 'more information' and allow it to be run.
2. Click on the "NOAA Open Data" tab.
3. Select NEXRAD Level-II.
4. Choose your radar using the pulldown under the Amazon pulldown.
5. Enter the day of your data, keeping in mind that time is in UTC rather than local time. See the note about time above.
6. Click on "List Files" to list the data for that day.
7. Scroll down the file list to find the time at the start of the event you're working on and click on it. If all day, just click on the first file.
8. Click on the "Load" button near the bottom of the window. This will bring up the first image. Click on the magnifier icon under "File" menu to center the image.
9. That should bring up another small window called "Radial Properties". This is where you choose 'Moment:' which is measurement type, and radar 'Elevation' angle.
10."Radial Properties:Moment" should say "Reflectivity".
11. Go back to the "Data Selector" window and make sure the filename at the start of your event is highlighted. Scroll down to the time when your event ends. Hold down the shift key and click on the file at the time when your event ends. This should highlight all of the relevant files for your case study.
12. Click on the "Animate" button. This will open an anmiation window. Click on the green "Play" button and confirm that you have storm related radar data and not just ground clutter. The dBZ values should be in the green or higher color bars (> 20 dBZ).
13. While the animation is still running, click on the "Export Movie" button. That will bring up a "Save" window that has pulldowns like this.
14. First try to use the file type "mp4" for export. It is a compressed file type that works well with powerpoint, but WCT has problems with it sometime. If you get an error like this, then follow step 14.a. If not follow step 15. (See step 18 if your animation does not need to be stopped and you want to use "Animated GIF".)
14a. If you get the mp4 error, then choose either the file type "AVI Movie (Encoding:JPEG, Small File Size)" if your movie will be for more than a data extending over 2 hours, or choose "AVI Movie (Encoding Raw - No Compression, Large File Size)" for data extending over less than 2 hours. These AVI files may not be viewable by windows media player, but can be read into powerpoint using this tab and sequence "Insert:VideoThis Device ..", and powerpoint will probably need to format the video. Alternatively, you could use a AVI-mp4 converter like this to get an mp4 video format movie that should be readable by powerpoint.
15. Skip this step if you needed to do step 14a. Otherwise, read your mp4 video into powerpoint using the sequence "Insert:VideoThis Device .." .
16. Click on the video in powerpoint. You can make it start automatically when the slide is presented by using the menu item "Playback:Start:Automatically" and "Loop until Stopped" clicked to show the check mark.
17. Repeat steps 10-16 for "Radial Properties:Moment" = "RadialVelocity" and then for "Radial Properties:Moment" = "CorrelationCoefficient" to get their animations into powerpoint.
18. Note: It is also acceptable to use "Animated GIF" as an animation of your data in step 14 instead of "mp4", especially if your animation does not need to be stopped in to point out specific features.

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Assignment 7: Radar Meteorology

The goal of this quick-study active-note-taking discussion is to become familiar with meteorological radar used to detect precipitation and severe weather.
Examples are on this page for composite reflectivity and for the Reno NWS dual polarization radar measurements.
Example of Doppler image for Des Moines Iowa.

Submission is through webcampus. Copy these questions to MS word and work on them.
Be sure to give your sources for answers.
Basics:
1. What is the diameter range for raindrops?
2. What is the diameter range for drizzle drops?
3. What is the diameter range for cloud droplets?
4. What is the shape of raindrops?
5. Why don't raindrops get arbitrarily large?

Local Rain Measurements:
6. What is the rainfall rate equation?
7. How does a simple rain gauge work?
8. How does a tipping bucket rain gauge measure rain? (picture from here).
9. How does a disdrometer work?

National Weather Service Radar.
Weather radar presentation as powerpoint and as a pdf document for understanding radar and dbZ.

10. What is the name of weather radars used by the National Weather Service?
11. What is the wavelength range used by this radar?
12. Briefly, how does radar work to measure rain?
13. Calculate the size parameter x=2 pi * Raindrop Radius / radar wavelength.
14. What 'radiation regime' is the size parameter of question 13? Note that it is the same radiation regime that gives rise to the blue sky on a clear day. Note.
15. What is the basic relationship for radar backscattering in terms of number of raindrops per volume, back scattering strength, droplet diameter D, and radar wavelength lambda? Note.
16. Why must the radar be empirically calibrated for rainfall rate given question 15, and question 6?
17. How does Doppler radar work? What can be detected with it?
18. How does dual polarization radar work, and what can be detected with it?
19. What is the correlation coefficient as used in meteorological radar?
20. What does this correlation coefficient indicate?

UNR Micro Rain Radar (data example) (Real-time data) LITTLE VALLEY UNR RESEARCH STATION (data example) (Real-time data)

21. What are the wavelength and frequency of MRR-2?
22. Describe the reflectivity, mean Doppler velocity, and spectral width?
23. What is the radar bright band and how can it be determined by the radar?
24. Discuss the reflectivity,Doppler velocity, Spectral Width, and bright band for the Little Valley Research Station data.

Resources:

  1. Demonstrations and calculations:
    a. Fill the aquarium with enough water to use the ultrasonic cloud generator.
    b. Make 'raindrops' and have them fall into the aquarium. Note sound made and potential for bubble formation to make more sound.
    c. Show the piezo electric sound sensor method of measuring sound droplets. Make a data acquisition system to observe traces created by raindrops hitting the sensor.
    d. Calculate how many cloud droplets (diameter d) it would take to make a single raindrop (diameter D). Talk about the lack of ability for radar to 'see' the cloud droplets.

UNR Micro Rain Radar (MRR) current measurements. Little Valley current measurements.

Great discussion of radar and its applications. (local backup).
What's under the dome? Discusses also the rotation of the radar.
Notes on differential polarization and the correlation coefficient associated with it.
National Weather Service discussion of weather radar.
Understanding radar discussion from the weather underground.

 

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Assignment 6: Near-surface weather stations

Purpose:

Lab Report with the Following Contents:

Additional Resources For This Assignment:

1. Style guide for lab reports.

2. UNR and DRI atmospheric instruments and measurement sites.

3. Journal article describing a measurement campaign similar to ours.

4. Atmospheric Instruments Textbook: See Appendix A on lab reports
Free through UNR Library: Online textbook for atmospheric instrumentation.

5. Relationships for wind speed and direction calculations.

6. RM Young sonic anemometer wind direction for U, V, and W winds (horizontal and vertical components).

Related Resources:

7. Wind roses to show wind direction and speed in single graph. (Python script and example data for it from the UNR weather station.)

8. Acquire and plot surface weather measurements as a function of time and location. Example of December 2025 minimum and maximum temperatures.

9. Note that tipping bucket precipitation measurements can distort the timing of snow in winter months (snow melts and is measured during day light hours).


Assignments 1 - 5 Online (see webCampus)

Assignment 5 Online (see webCampus) precipitation estimates.

Purpose: Become familiar with precipitation estimate measurements.

Assignment 4 Online (see webCampus) atmospheric radar measurements.

Purpose: Introduction to radar use in meteorology.

Assignment 3 Online (see webCampus) measurement of wind.

Purpose: Become familiar with atmospheric wind measurements.

Assignment 2 Online (see webCampus) measurement of atmospheric temperature.

Purpose: Become familiar with atmospheric temperature measurements.

Assignment 1 Online (see webCampus) Overview of Atmospheric Instrumentation.

Purpose: Broad overview of atmospheric instrumentation measurements.
This is an online homework assignment and is described on webCampus.



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