While its name sounds very intimidating, the CAPS measures a component common amongst some of the aerosol instrumentation ARM employs. Namely, the optical extinction (sum of absorption and scattering) of light through a sample of aerosols, as given by Beer's Law. While the CAPS instrument systems operating at SGP E13 and ENA C1 measure this optical extinction at RED , BLUE and GREEN visible wavelengths, the CAPS currently deployed at OLI M1 only measures extinction of a RED visible wavelength of (630 nm).
As of now, please monitor the b1-level aoscaps and aoscaps3w (SGP E13 and ENA C1) datastreams. When submitting DQPRs for the CAPS, please use the CAPS-PMEX instrument class under the AOS Group.
For more information, please see the CAPS Instrument web page. You can also find more technical CAPS documentation at the vendor's website. For those that want to wade into the underlying cavity attenuated phase shift spectroscopy instrument theory, see this article.
The CAPS is a component instrument within the Aerosol Observing System (AOS). For a more complete overview the AOS system and its general backing measurement theory, please see the AOS DQ Wiki page.
In the metrics table below, there is one primary measurement field; all other measurements are diagnostic in nature. That primary field is:
Note: The Bext_R field is operationally missing for short periods of every hour, as reflected in the above QC metrics table. This is in-line with expected operations (related to impactor switching) and does not need to be noted in your DQAs.
In the metrics table below, there are three primary measurement fields; all other measurements are diagnostic in nature. Those primary fields are:
The primary 1- and 3-wavelength CAPS measurements are those of the extinction (sum of scattering and absorption) coefficient of light at a given wavelength. For the 1-wavelength CAPS (aoscaps; OLI M1), the extinction coefficient for the CAPS is only measured at a nominal red wavelength (630 nm); these extinction coefficients are measured at nominal red, blue and green wavelengths for the 3-wavelength CAPS (aoscaps3w; SGP E13 and ENA C1). The plots below show time series of these measured 1-wavelenth CAPS (first) and 3-wavelength CAPS (second) extinction coefficients at these wavelengths.
As all CAPS instrument systems are plumbed to the AOS Impactor, these extinction coefficients are parsed according to the impactor_state setting (either 1- or 10-micrometers) for the daily extinction coefficient plot. These two impactor settings are indicated by the different colors and the annotated text in the plotting window for convenience. Note that to first order, extinction coefficients associated with the 1-um impactor setting (smaller aerosol particles) are lower than those associated with the 10-um impactor setting (larger aerosol particles). That is, larger particles generally extinguish (scatter and absorb) more visible light than do their smaller counterparts. A question for further thought - would this always be the case?
Note that impactor setting parsing is not currently performed for the weekly extinction coefficient plot. There, the user is seeing the full time series of extinction coefficients, regardless of impactor setting switching.
In addition to the primary extinction coefficient measurements, the DQ Office plots a number of diagnostic fields to monitor general instrument health. These include diagnostic instrument pressure and temperature and the signal level of the CAPS light source (light signal level). Note that because the CAPS is plumed to the AOS impactor, the diagnostic CAPS instrument pressure should toggle in response to impactor setting (see first panel of diagnostic plots below). Namely, CAPS pressures should be higher in association with a 10-um impactor setting, and vice versa; major deviation from this behavior could indicate a problem with either the impactor or the CAPS and is grounds for DQPR submittal.
No known behaviors that do not require DQPR's or mentions in DQA's. Document some here.
Dirty optics can lead to questionable data for the CAPS. It is important to keep an eye out for these issues, and note them in your DQAs if you do see them (a DQPR may be required as well). In the case of DQPR 5213, a tear in the purge lines caused the dirty optics (the purge lines are responsible for keeping the mirrors clean). This can cause negative extinction coefficients, which are unrealistic. If you see negative extinction coefficients then something is potentially wrong.
Failing pumps can lead to severe flow irregularities that severely compromise the data. Signs of a failing pump include more noise in the CAPS extinction coefficient data. If you see noisier CAPS extinction coefficient data, you should mention it in your DQAs. See DPQR 5738 for an example of this issue.
Periodic negative extinction coefficients can also appear due to interference from anthropogenic emissions (in the case of DQPR 5807, the culprit was NO2).