¶ Sky Radiometers on Stand for Downwelling Radiation (SKYRAD)
¶ Instrument Description
The Sky Radiation (SKYRAD) collection of radiometers provides each Atmospheric Radiation and Cloud Station (ARCS) with continuous measurements of broadband shortwave (solar), longwave (infrared), and ultraviolet irradiances for downwelling components.
SKYRAD Sky Stand Picture of the instruments used to create the datastream. The rotating platform will track the movement of the sun and is called the tracking stand. Each black ball will shade the direct radiation for the DS (down_short_hemisp) and DIR (down_long_hemisp_shaded 1 & 2). ->
- For more information see the SKYRAD Instrument web page.
¶ Additional Information
¶ Instrument Table
Below is a table of the 4 Radiometer Types and Functions.
| Field | Measurement | Code | Radiometer | Location |
|---|---|---|---|---|
| down_short_hemisp | Downwelling Shortwave | DS | Pyranometer Model PSP (Clear Domes | Metal Post (On Horizontal Plate Inside Ventilator) |
| down_short_diffuse_hemisp | Downwelling Diffuse Shortwave | DD | Pyranometer Model PSP (Clear Domes) | Solar Tracker (Under Shade Disc Inside Ventilator) |
| short_direct_normal | Direct Normal Shortwave | NIP | Pyrheliometer Model NIP | Solar Tracker (On Side Bracket) |
| down_long_hemisp (formerly: down_long_hemisp_shaded) | Downwelling Longwave | DIR | Pyrgeometer Model PIR (Silver Dome) | Solar Tracker (Under Shade Disc Inside Ventilator) |
PSP = Precision Spectral Pyranometer (an Eppley Laboratory, Inc. designation, aka 8-48 Black and White)
NIP = Normal Incidence Pyrheliometer
PIR = Precision Infrared Radiometer
Most often the data will be of a reasonable level and withing expected range. To give you a general view of what to expect, here is a table of values for each measurement with four different clear sky levels. Without a TSI, it will be a guestimate as to what the actual amount of cloud cover is at any given moment.
| Data Code | Clear Sky Low Sun |
Clear Sky High Sun |
Cloudy | Night | Comments [Physical Limits] |
|---|---|---|---|---|---|
| DS | 300 - 500 | 600 - 1100 | 100 - 550 | -10 to 5 | Values can rapidly fluctuate under partly cloudy sky [0 to 1367 (solar constant)] |
| DD | 50 - 200 | 50 - 200 | 100 - 550 | -10 to 5 | DD will increase slightly with cloud amount [0 to 500 under white clouds] |
| NIP | 300 - 700 | 700 - 1100 | -10 to 5 | -10 to 5 | Shadows indicate NIP is greater than 200 [0 to 1367 (solar constant)] |
| PIR | 350 - 450 | 350 - 450 | 300 - 400 | 350 - 500 | Clouds (day or night) will increase longwave [-40°C => 167 Wm-2] |
Derived DS values will often differ slightly from your actual ones. They will usually stay within 50 W m^-2 of each other; however, rapid changes in the atmosphere can create rather large gaps. These do not need to be noted unless the difference is greater than +/- 200 W m^-2 briefly, or greater than +/- 100 W m^-2 for several hours.
¶ Expected Operations
¶ Metrics
¶ Plots
¶ Primary Variables
The skyrad plot includes:
- Shortwave direct normal solar irradiance (sdn), downwelling shortwave diffuse horizontal (sky) solar irradiance (dsdh), downwelling shortwave hemispheric (dsh) (or total hemispheric (global) solar irradiance), and derived dsh
- Difference between the derived downwelling shortwave hemispheric and downwelling shortwave hemispheric solar irradiances
- Ratio of derived downwelling shortwave hemispheric and downwelling shortwave hemispheric solar irradiances
- Sky/cloud IR Temperature (IRT)
- Downwelling longwave hemispheric for "hemisp1" instrument and "hemisp2" instrument
- Battery Voltage
On a completely sunny day, the SDN and DSH should peak around solar noon. The DSDH should be low and remain fairly constant throughout the day. The peak downwelling longwave hemispheric irradiance should occur slightly after solar noon.
NOTE: A weekly plot also exists for each of the above SKYRAD panels.
The following plots depict the 30 day nightly average of the derived DSH - DSH, as well as the nighttime derived DSH - DSH.
¶ Comparison Plots
The following comparison plot is the same plot used in the GNDRAD comparison plots. It includes data from both the SKYRAD and GNDRAD instruments. The values between SKYRAD and GNDRAD will not compare one to one, but should generally trend the same.
¶ Site-Specific Information
SKYRAD is located at NSA and ENA. NSA has some interesting working conditions, and often can create interesting conditions. Here are some examples from NIMFR.
¶ Known Issues
¶ Known Behaviors
There are currently no known behaviors for this instrument. Document some here.
¶ Past Problems
List of past problems for this instrument that DO need to be mentioned in your DQA's:
Solar Noon spike
Spike due to obstruction
down_short_hemisp and down_short_diffuse_hemisp swapped
