Atmospheric analysis

Technical Note No. 98/2 - Hardware Control Options Explained: Conversion of Volts to Pressure, DOBIE Calibration, Sensor Noise Conversion of Volts to Pressure DOBIE converts volts to pressure by:
where p is pressure in pounds per square inch, V is volts output by the pressure sensor, G is gain (units of psi/volt) and O is offset (units of psi).

Technical Note No. 98/1 - At What Depth Should DOBIE be Deployed? To answer the question, we need to explain what DOBIE actually measures and how waves exert pressure at depth. DOBIE measures pressure. In still water, the pressure experienced at depth is composed of two parts: hydrostatic pressure, which is due to the weight of the overlying water and which is proportional to the height of the water column above the observer, and atmospheric pressure, which is due to the weight of the atmosphere.

Technical Note No. 99/1 - Measuring Waves in Lakes and Estuaries is Quite Tricky, data can be Improved by Adjusting Sensor Noise Level
It sounds paradoxical, but the most difficult task when measuring waves (Task 4/0 or Task 4/1) is knowing when there aren't any! The danger is that sensor noise - not real signal - gets transformed into estimates of wave height, which will be wrong. The "reality checks" applied by DOBIE have been described in a previous Technical Note, and these are meant to catch those bursts where sensor noise has been (incorrectly) transformed.

Technical Note No. 2000/1 - Conversion of Hydrostatic-Depth Spectrum to Sea-Surface-Elevation Spectrum Since the release of version 19.5, PEDP reports beside each spectral estimate Sh(f) when processing Task 4/1 spectra. is defined as:
where z* is the depth of DOBIE below mean water level, is the mean water depth and k is the wavenumber corresponding to f, the frequency of the spectral estimate.

NIWA's mobile air quality monitoring trailers contain equipment capable of measuring a range of key air contaminants and meteorological parameters.

Modern marine geoscience requires accurate and detailed subsurface information for the mapping of geologic structures and sedimentary sequences beneath the continental margin. In order to acquire this information NIWA purchased a Multi Channel Seismic system (MCS) in December 1996, consisting of a 24 channel streamer, seismic source and acquisition hardware. 

NIWA has been engaged in an active UV research programme since the 1980s. The cornerstone of this work is the routine accurate measurement of the spectrum of surface UV irradiance to quantify UV climatologies, to understand the causes of UV variability (temporally and spatially), and to monitor long-term changes.

Sometimes it is neccessary to disconnect fibre and diffuser. Reconnection can cause a change in the diffuser-fibre distance, which could lead to errors in previous calibrations. Thermal expansion can also be a reason for a changing diffuser-fibre distance .
The following graph shows the change in photomultiplier signal due to a changing fibre distance.
When the fibre is relocated with care relocation errors are around 0.1mm.

Setup
The following setup was used for testing the cosine response and transmission of the diffuser.
In this setup the lamp distance is as large as possible. The reason for this is that the lamp should resemble a point light source. If the lamp is placed at a close distance this would lead to large errors especially at bigger zenith angles. The diam eter of the windings inside the lamp are about 5 mm. A high accuracy power supply is used to keep the lamp current constant (Optronics OL 83A). The voltage across the lamp filament is monitored directly.

PTFE is an excellent diffuser material for instruments exposed to the elements: It has a low coefficient of thermal expansion (0.000122mm per degree Celcius) It has a low moisture absorption (< 0.01%) It is stable against damage by UV radiation The following graph shows the measured temperature-sensitivity of teflon for the temperature range 19 degrees Celcius and 45 degrees Celcius.
Info, questions and remarks, contact:
Richard McKenzie [ [email protected] ]