¶ Shortwave Array Spectroradiometer-Hemispheric (SASHE)
¶ Instrument Description
The Shortwave Array Spectroradiometer – Hemispheric (SASHE) uses a hemispheric spectralon diffuser and rotating shadowband similar to the MFRSR and RSS instruments, so it also provides spectrally resolved, direct-normal, diffuse-horizontal, and total-horizontal irradiances, and can be calibrated in situ via Langley regression. The SASHE incorporates two Avantes fiber-coupled spectroradiometers (Avaspec ULS 2048 CCD and Avaspec NIR256-1.7) for visible and near-infrared detection in the wavelength range 350–1700 nm. The spectral resolution is 2.4 nm for the ULS 2048 CCD and 6 nm for the NIR256-1.7. Like the SWS and SASZE, an external collector mounted outdoors is connected via fiber optic cable to a pair of spectroradiometers housed indoors, so the entire spectral range is measured simultaneously for both spectroradiometers. For the typical shadowband measurement, the spectroradiometers are operated with 1 measurement per second, but the entire shadowband sequence takes about 20 seconds so this is the measurement interval for the irradiances. The SASHE operating sequence is configurable and supports alternate programmed sequences as a function of solar zenith angle. For example, it currently employs different sequences for high-sun angles, low-sun angles, and twilight conditions when the sun is below the horizon but the sky is not yet fully dark, and includes a mode where visible spectra are collected rapidly while the band is moved over range of near-sun angles to characterize the forward scattered radiation.
- For more information see the SASHE Instrument web page.
¶ Additional Information
The SASHE data are preliminarily calibrated through comparison with calibrated lamps. The accuracy of irradiance produced by the SASHE is expected to be better than ±5%, which includes calibration and instrument stability errors. Under suitably uniform atmospheric conditions, higher calibration accuracy and precisions (±1%) can be obtained when the responsivity is tied to the solar extraterrestrial irradiance via Langley regression plots. This approach is recommended when high precision measurements of optical depth are required.
- For more information see the Radiation Information Page.
¶ Expected Operations
This instrument does not record radiance overnight so data will be unavailable (orange) during those hours.
¶ Metrics
SGP
- Data is not available overnight.
- There are typically various DQO flags throughout the day when data falls below zero.
- The integration_time_spectrometer_vis is missing all day.
AMF1
- Data is not available overnight.
- There are typically various DQO flags throughout the day when data falls below zero.
¶ Plots
SASMFR
- This set of plots of the Direct Horizontal radiation, Diffuse Hemispheric radiation, Direct Normal radiation, and Total Hemispheric radiation.
- Each of the 4 radiation plots are recorded at 415nm, 500nm, 615nm, 673nm, 870nm, and 940nm.
- These plots are compared against the MFRSR and NIMFR (AMF1 only compares against the MFRSR).
SASHEVIS
- These plots are a cross section of the wavelength of each of the 4 radiation plots above within the visible spectrum.
- On clear days (such as this one) each plot should be ovular with the peak wavelengths at solar noon.
- On cloudy days incoming radiation will be less and/or patchy and these plots will become messier.
SASHENIR
- These plots are a cross section of the wavelength of each of the 4 radiation plots above within the near infrared spectrum.
- On clear days (such as this one) the direct horizontal and total hemispheric plot should be ovular with the peak wavelengths at solar noon while the diffuse hemispheric and direct normal may have very little data visible.
- On cloudy days incoming radiation will be less and/or patchy and these plots will become messier.
atmos_pressure
- This is a plot of the atmospheric pressure compared against the local MET (E13 at SGP).
diagnostic_temp
- Plots of the collection, chiller, and avantes diagnositc temperatures.
mio_temperatures
- Plot of the multi-IO temperature trh (green) and mems (blue).
diagnostic_rh
- Plot of the spectrometer chiller internal RH (green) and the mulit-IO RH (blue).
diagnostic_dewpoint
- Plots of the chiller dewpoint and collector internal dewpoint.
collector_tilt
- Plot of the collector Y tilt (green) and X tilt (blue).
- Plots of the collector X and Y tilts standard deviation.
solar_angles
- Plots of the band azimuth angle (green) and zolar azimuth angle (blue).
¶ Site-Specific Information
The SASHE is currently located at SGP C1 and AMF1. All locations operate similarly.
¶ Known Issues
¶ Known Behaviors
List of known issues for this instrument that MAY NOT need to be mentioned in your DQA's:
Higher channel poor comparison
- The higher channels, particularly the 870nm and 940nm channels, do not typically compare well with the MFRSR or NIMFR. They should, however, trend the same as those instruments.
¶ Past Problems
List of past problems for this instrument that DO need to be mentioned in your DQA's:
Negative direct data
- When the instrument shader becomes misaligned the direct data can become negative and reversed of the MFRSR direct data.
