This document describes the operation and measurements of the Integrated Surface Flux Facility (ISFF) and ATD SODAR during the scintillometer test for the Advanced Technology Solar Telescope (ATST) at the Boulder Atmospheric Observatory (BAO) near Erie, Colorado in January, 2004. The first sections are from the planning document (hence the use of present/future tense).
A $160 Million effort is underway to build the last large (4m) solar (viewing the sun; obviously during the day) telescope. This telescope will have about 1000 actuators to dynamically adjust for atmospheric interference, but they have limitations, so it is necessary to site this scope where atmospheric turbulence (characterized by the refraction structure parameter, C_n^2) is minimal.
Data have been taken at 6 candidate sites over the past 2 years using two types of scintillometers, but are highly sensitive to corrections used in the near-field of view of these instruments. The magnitude of these corrections is enough to change a site from being determined to be usable to unusable or vice versa.
Thus, a verification data set is needed to determine if any of these correction schemes produce values which are good enough for site evaluation. In situ measurements (either from a tower or balloon) of C_n^2 (from C_T^2 and C_q^2) should produce unambiguous results. Sodar measurements of C_n^2 also may provide adequate measurements.
We agreed that a deployment near a tower would be useful and selected the BAO as a readily available and accessable location. This deployment would feature:
- ATD Sonic anemometer/thermometers and krypton hygrometers to measure T and q fluctuations to produce C_T^2 and C_q^2 (and thus C_n^2). These sensors could be at any location on the BAO -- we might select as overlapping with the SODAR. We could measure at 1 and 5m as well.
- The ATD sodar to measure C_n^2 from accoustic reflectivity.
- One set of the scintillometers that was used at one of the 3 candidate sites which have been rejected in the meantime.
ATD would deploy CSAT sonic anemometer/thermometers and krypton hygrometers at 5-8 levels (5, 10, 20, 50, and 100m, and possibly 2, 200, and 300m) on the BAO tower (assuming that we can get permission from NOAA/ETL). (See sensor layout.) It would not be advisable to attempt an inertial subrange measurement (needed for C_T^2) below 2m with the sonic anemometers due to path averaging.
In order to compute T and q from Tc and kh2o, we will need average T, RH, and P data. These may be available from the BAO. Alternately, we could deploy a TRH and barometer (consuming another 2 serial channels).
The krypton data would be ingested using our "serializer"s. The serializers could be either the HC11-based ones we used in IHOP/HVAMS or a new version based on the Tern or other processor. Either would have to be repackaged (into the CSAT electronics box??) and some cables may have to be made. Thus, a single serial data stream would need to be ingested from each level. We could use our existing cabling to get data from sensors at 2, 5, 10, and possibly 20m. For the higher levels, we would "tap into" existing BAO cabling if possible, or use our Freewave RF modems to get data down the tower.
At the base of the tower, we would need some way of ingesting 5-8 serial data streams. The easiest solution would be to use a laptop with an Edgeport, running Gordon's test ADAM code. (We could also try the Prometheus instead!) This code is "hard-configured", but already works for CSAT sonics and should be readily changed to add the krypton data from a serializer. This system should be networked back to Boulder. Presumably, some sort of workable network connection is available at the BAO. If not, we could implement a PPP link via another Freewave back to FLAB, but this could be more work. A housing (chem shelter/cooler??) would have to be figured out for the laptop.
Data will be taken during the month of January or until 7 days of reasonable conditions were collected (whichever comes first). Fortunately, this study only wants data during clear-sky conditions so data during precipation are not needed.
Hopefully, booms exist on the BAO for sensor mounting. We also assume that power is available at each measurement level. The sonics should require little maintenance and do not need to be calibrated. The kryptons probably need to be calibrated prior to set-up. (They have been recently "post-calibrated" after HVAMS, but we may chose to change the pathlength for winter in Colorado.) After fog/dew/precipitation events, the kryptons would need to be cleaned. This maintenance would be done by HAO or RAP staff (Jeff Cole??). The TRH would also require calibration. The current barometer calibration should be adequate.
These data will be analyzed within 2 weeks to produce C_n^2 values for comparison with the other measurements. The data analysis will be done jointly between ATD and HAO staff so that HAO staff could look at future data (if necessary). We would need to write code to generate TIME SERIES of T and q from Tc and kh2o. This should be doable as one-time code in S. C_T^2 and C_q^2 are the amplitudes of the autocorrelation functions of T and q. We have S+ code to generate these functions. It would be run in reasonably fine time steps (1 minute?), since the intertial subrange only exists at high frequencies.
In the case that no meaningful relation can be obtained with the scintillometer data, it would be necessary to make tower and/or sodar and/or tethersonde measurements at each of the 3 site candidates which are now under consideration (Big Bear Lake, CA; Maui, HI; or La Palma, Canary Islands). In this case, HAO would arrange to rent/purchase the necessary equipment.
- Jan 5, 2004
- Jan 8, 2004
- Full sodar operations start
- Jan 9, 2004
- Full tower operations start
- Jan 31, 2004
ISFF will instrument several levels of the NOAA BAO tower.
For a complete description of this tower, see here.
Our GPS readings of position are:
|300m||40deg 03'00.0" = 40.050deg||105deg 00'13.7" = 105.004deg W||1577m|
|5m||40deg 03'00.2" = 40.050deg||105deg 00'17.8" = 105.005deg W||1569m (probably not correct)|
Layout of ISFF sensors on the BAO and a small auxilliary tower. Sensors were at heights of 5, 10, 22, 50, and 100m.
Each of the instrumented levels had:
In addition, at 5m:
- Vaisala 50Y Humitter to measure air temperature and RH; in an NCAR aspirated radiation shield
- Barometer, Vaisala PTB220B, with a single-disk static pressure port
for the measurement of state variables. T, RH, and wind speed and direction also are being measured by NOAA at 10, 50, and 100m.
The SODAR (a Metek DSDPA.90-24) was deployed at the outer tower guy point, approximately 260m South of the BAO tower. It will produce profiles of Cn^2_accoustic at as high spatial resolution as possible (5--10m).
ISFF Field Logbook
A computer-readable field logbook of comments by NCAR and other personnel is available in read-only html form.
ISFF QC Plots
Click on the above link to view plots from the ISFF sensors on the BAO tower.
5 minute statistics for most variables are shown on 48-hour time-series plots.
Spectra plots of high-rate data from 00:00-00:30 and 12:00-12:30 local time each day are provided as available.
- Steve Oncley and Tom Horst description of the Cn^2 calculation.
- Hill et al. paper with results from this study.
- Advanced Technology Solar Telescope
- Boulder Atmospheric Observatory