Instruments and measurements method

Downward irradiace at the sea (land) surface Ed_pyr(lambda) is measured by pyranometers (thermopiles). The output voltage signal is amplified, integrated over 30 s and transformed into irradiance units

The following pyranometer models have been in use:

  1. Yanishevsky pyranometer (prod. USSR, Gidrometrpribor, Tbilissi),
    total solar irradiation: (300-2800 nm)
    measurement precision: 10%,
  2. Kipp&Zonen pyranometer (the Netherlands), model CM-5
    total solar irradiation 300-2800 nm,
    measurement precision 8%
    sensitivity 9-15 microV/Wm-2
    impedance 70-100 Ohm
    response time (1/e value) 5 s
    99% value after 55 s
    ambient operating temperatures -40 to +60 deg C
    max irradiance 2000 W/m2
    cosine response < -/+ 7% (percentage deviation from ideal at 10 deg solar elevation on a clear day)
    azimuth response < -/+ 5% (percentage deviation from the mean at 10 deg solar elevation on a clear day)
    nonlinearity -/+ 2% (percentage of full scale)
  3. Pyranometer by Eppley Laboratory Inc. (USA) model PSP (Precision Spectral Pyranometer)
    measurement precision 5%
    total solar irradiation 295-2800 nm or in defined wavelength bands dependent on a type of Schott fitler used: WG295 (295-2800 nm), GG395 (395-2800 nm), GG495 (495-2800 nm), OG530 (530-2800 nm), OG570 (570-2800 nm), RG610 (610-2800 nm), RG630 (630-2800 nm), RG695 (695-2800 nm), RG715 (715-2800 nm), RG780 (780-2800 nm).
    sensitivity 9 microV/W m-2 approx.
    impedance 650 Ohm approx.
    receiver circular 1 cm-2, coated with Parsons' black optical laquer
    linearity -/+ 0.5% from 0 to 2800 W/m2
    temperature dependance -/+ 1% over ambient temperature range -20 to +40 deg C
    response time (i/e value) 1 s
    cosine -/+ 1% from normalization 0-70 deg zenith angle
    orientation no effect on instrument performance

Measurement precision under the conditions of low solar radiation level (<100 W/m2) or low solar altitude (h < 20 deg) may be lower than given above. Apart from the errors caused by the pyranometers precision and the instability of the electronic unit (especially amplifiers) the main sources of the measurement errors on the ship are: low precision of instruments levelling and shading by the masts (r/v Oceania case). The influence of the list and well as rolling and pitching of the ship is considerably reduced by mounting the pyranometers on Cardan suspensions.
Three Eppley pyranometers are mounted on a common platform with Cardan suspension and a levelling device.
Kipp&Zonen pyranometer is placed on a separate Cardan suspension without a levelling device, 2 m from the Eppley's.
The measurement precisions given above comprise all the error sources except shading by the masts.