¶ Microwave Radiometer, High Frequency (MWRHF)
¶ Background
The Microwave Radiometer-High Frequency (MWRHF) provides time-series measurements of brightness temperatures from two channels centered at 90 and 150 GHz. These two channels are sensitive to the presence of liquid water and precipitable water vapor.
¶ Additional Information
Please review Brightness Temperatures for more information of the fields measured by this instruments.
For more information see MWRHF.
¶ Expected Operations
¶ Metrics
¶ Plots
Quality Checks
Listed below are some of the quality checks that the instrument mentor performs. She submits a monthly report summarizing her findings. It would also be beneficial for you, the student analyst, to keep an eye out for any values that may fall outside the bounds of these checks:
- In general, the brightness temperature time series should be smooth and with low noise levels. These can be checked by glancing at the brightness temperature plots. Are there any abnormal spikes, or too much noise?
- Brightness temperatures should be greater than 2.75 K and less than approximately 330 K. The embedded QC should already catch this, and will flag as bad data under the tbsky90 and tbsky150 rows of the MWRHF metrics table.
The following can be observed by looking at the MET MWR3C comparison plots:
- External temperature readings can be compared to tower measurements. The agreement should be +/- 2 K.
- External pressure readings can be compared to tower measurements. The agreement should be +/- 5 KPa.
- External relative humidity readings can be compared to tower measurements. The agreement should be +/- 5%
Sky Brightness Temperatures
These are the sky brightness temperatures for the 150 and 90 GHz channels. They will increase in the presence of cloud and precipitation. There is a flag plotted when the instrument detects that there is water on it. These 2 variables should trend together.
Meteogram
The MWRHF also has sensors to measure some surface meteorological variables, suchas Temperature, Relative Humidity, and Pressure. There is a comparison plot with the co-located MET to better determine if there is a problem with one of these sensors.
Tip Totals
The MWRHF collects "Tip Curves" every hour to perform a calibration. This is also dependent on if the conditions are right. Each channel does it separately, so they will have a different number of tips. The total number of tips per day are plotted out in this plot. The 150 GHz channel normally does not perform nearly as many tips as the 90 GHz channel.
Tip Curves
Data collected from these calibrations are also plotted. This is mostly for the mentor to review.
¶ Comparison Plots
Meteogram Comparison
Data from the MWRHF and co-located instruments are plotted up. Depending on the site, it will include the MET and the ECOR. The MWRHF will actually be a little off from the other instruments. These are secondary sensors on the MWRHF and are not nearly the quality of the MET sensors. They should still trend the same though.
Sky brightness temperature comparison
Any radiation instrument that measures sky brightness temperature is being plotted, if available. This is more to make sure that all the instruments are trending together, so don't pay attention to the y-axis scale. This is also plotted out over 1 week.
LWP/PWV comparison
The liquid water path and precipitable water vapor are being calculated from the MWRHF and compared with other instruments onsite that measure LWP/PWV or that it can be calculated from.
MWR3C Comparison
¶ Site-Specific Information
This instrument is located at all sites.
¶ Known Issues
¶ Known Behaviors
Known issues for this instrument that MAY NOT need to be mentioned in your DQA's:
Sun in field of view of instrument
The MWRHF, like the MWR and MWR3C, views a narrow field of view directly above the instrument. As the sun tracks north-south throughout the year, it can align directly within the field of view of the instrument, when the sun is directly overhead. This will cause a bump in brightness temperatures, LWP,and PWV centered on local solar noon (yellow dashed line on plots). There is no quality to resolve. Just note this in the DQA's. Typically the instrument mentor will issue a DQR for the affected data (about 1 hour per day for about three weeks). Notice the spike in brightness temps from approximately 13:00 to 13:30 UTC below:
¶ Past Problems
Past problems for this instrument that DO need to be mentioned in your DQA's and possibly requiring a DQPR submittal:
Noise of 150GHz channel
Failed Heater
Any time the heater fails to work, condensation can accumulate on the window, especially during night time and early morning (and particularly during times of high humidity). Data affected by condensation on the window can be found by observing a smooth and steady increase in the brightness temperature(s), followed by a smooth and steady decrease. Relative humidity during these times is typically 70% or higher. See the example plot below:
Rain Sensor Failure
| A failure of the rain sensor can cause the rain flag to always stay on, even if it isn't raining. When the rain flag is on, the radiometer will not perform tip curves, and thus will not be able to calibrate properly. If you find yourself suspicious of a rain flag that stays on for a long period of time, it is a good idea to check the rain flag indicators of a nearby MWR, MWRP, MWR3C, etc. If they are not flagging nearly as often as the MWRHF, that is an indication that something is wrong. See DQPR 2542 for more information. |
| The rain sensor can also malfunction and fail to pick up precipitation, even if it is raining. An issue like this would also be fixed with a installing a replacement sensor. Once again, an easy way to scope an issue like this out would be by comparing the rain flag of the MWRHF to nearby rain flags of an MWR, MWRPW, or MWR3C. |
Incorrect Ambient Surface RH
Occasionally, the surface RH temperature recorded by the MWRHF will not compare well with co-located RH instrumentation. In this case, a new sensor fixed the problem. See example plots below (note that the humidity was consistently reading too high (>110%) :
Obstructions in field of view
Obstructions in the field of view of the MWRHF can cause abnormal spikes in the TBSKY channel data. Re-orienting the radiometer may help, but if the field of view is not clear in any direction, it may not be possible to fix the issue. However, if the spikes are occasional, the data may still be usable (it is still a great idea to mention this in your DQAs, and possibly in a DQPR, though). Notice the intermittent spikes in the TBSKY90 data as an example below:
