2013/02/09

What Affects DLWIR?

Using the same data source as before, the same parameter nulling gives this set of curves


This is the variation of DLWIR with day of the year (as before but low prob results retained)

This is absolute humidity effect - not linear

Interesting (night is disabled - no cloud information) but DLWIR is greater in mornings and evenings.  Why not midday?

Station Pressure - Possibly a problem with conversion between % hum and abs humidity causes this.

Linear effect with temperature as would be expected

Again a non linear relation with ULWIR
Wild errors are removed from the result by using the trimmean funcion disposing of 25% of highest and 25% lowest values.
Cloud values are measured using a visual light camera - hence no results will be returned for hours of darkness for this analysis.

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Instrumentation
u/dlwir
PRECISION INFRARED RADIOMETER
Model PIR
The Precision Infrared Radiometer, Pyrgeometer, is intended for unidirectional operation in the measurement, separately, of incoming or outgoing terrestrial radiation as distinct from net long-wave flux. The PIR comprises a circular multi-junction wire-wound Eppley thermopile which has the ability to withstand severe mechanical vibration and shock. Its receiver is coated with Parson's black lacquer (non-wavelength selective absorption). Temperature compensation of detector response is incorporated. Radiation emitted by the detector in its corresponding orientation is automatically compensated, eliminating that portion of the signal. A battery voltage, precisely controlled by a thermistor which senses detector temperature continuously, is introduced into the principle electrical circuit.
Isolation of long-wave radiation from solar short-wave radiation in daytime is accomplished by using a silicone dome. The inner surface of this hemisphere has a vacuum-deposited interference filter with a transmission range of approximately 3.5 to 50 µm.
SPECIFICATIONS
Sensitivity: approx. 4 µV/Wm-2.
Impedance: approx. 700 Ohms.
Temperature Dependence: ±1% over ambient temperature range -20 to +40°C.
Linearity: ±1% from 0 to 700 Wm-2.
Response time: 2 seconds (1/e signal).
Cosine: better than 5%.
Mechanical Vibration: tested up to 20 g's without damage.
Calibration: blackbody reference.
Size: 5.75 inch diameter, 3.5 inches high.
Weight: 7 pounds.
Orientation: Performance is not affected by orientation or tilt.
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This looks as if it is measuring the heating effect (thermopile) of radiation hitting the dome of the sensor (transmission 3.5 to 50um. The thermopile of course generates a voltage dependant on the temperature difference between one side and the other The non-dome side is not exposed to external radiation so no effect there. However, the nondome side temperature must be measured and compensated.
The instrument also compensates for its own generated IR.
No assumption of BB radiation is assumed. It is the ACTUAL heating effect of IR radiation of narrow or wide bandwith hitting the sensor that is the cause.

If the radiative "temperature" is less than the receiver temperature then the thermopile still measures - see series of posts about thermal imaging - the camera microbolometers sitting at 20+C shows temperatures down to -40C

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Dry bulb temperature / wet bulb / relative humidity

HMP45C-L Specifications

  • Supply Voltage: 12 Vdc nominal (typically powered by datalogger)
  • Current Drain: ≤4 mA (active)
  • Sensor Diameter: 2.5 cm (1 in.)
  • Sensor Length: 25.4 cm (10 in.)
  • Cable Diameter: 0.8 cm (0.3 in.)
  • Weight: 0.27 kg (0.6 lb)

Relative Humidity

  • Sensor: Vaisala’s HUMICAP® H-chip
  • Measurement Range:
    0.8% to 100% RH, non-condensing
  • Output Signal Range:
    0.008 to 1 Vdc
  • Accuracy at 20°C (against factory reference): ±1% RH
  • Accuracy at 20°C (field-calibrated against references):
    ±2% (0% to 90% RH);
    ±3% (90% to 100% RH)
  • Temperature Dependence: ±0.05% RH/°C
  • Long-Term Stability: Typically, better than 1% RH per year
  • Response Time: 15 s with membrane filter (at 20°C, 90% response)
  • Settling Time: 500 ms

Temperature

  • Temperature Sensor: 1000 ohm Platinum Resistance Thermometer
  • Measurement Range: -39.2° to +60°C
  • Output Signal Range:
    0.008 to 1.0 V
  • Accuracy:
    ±0.5°C (-40°C),
    ±0.4°C (-20°C),
    ±0.3°C (0°C),
    ±0.2°C (20°C),
    ±0.3°C (40°C),
    ±0.4°C (60°C)
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Cloud - total and opaque

TSI-880 AUTOMATIC TOTAL SKY IMAGER

General Description The Total Sky Imager Model TSI-880 is an automatic, full-color sky imager system that provides real-time processing and display of daytime sky conditions. At many sites, the accurate determination of sky conditions is a highly desirable yet rarely attainable goal. Traditionally, human observers reported sky conditions, resulting in considerable discrepancies from subjective observations. In practice, the use of human observers is not always feasible due to budgetary constraints. The TSI-880 now replaces the need for these human observers under all weather conditions.
An onboard processor computes both fractional cloud cover and sunshine duration, storing the results and presenting data to users via an easy-to-use web browser interface. The self-contained design makes it well suited for mission-critical applications such as aviation and military meteorology monitoring. It captures images into standard JPEG files that are analyzed into fractional cloud cover; if networked via TCP/IP (10/100BaseT) or PPP (modem) it becomes a sky image server to remote any user via the web.

TSI-880 AUTOMATIC TOTAL SKY IMAGER

General Description The Total Sky Imager Model TSI-880 is an automatic, full-color sky imager system that provides real-time processing and display of daytime sky conditions. At many sites, the accurate determination of sky conditions is a highly desirable yet rarely attainable goal. Traditionally, human observers reported sky conditions, resulting in considerable discrepancies from subjective observations. In practice, the use of human observers is not always feasible due to budgetary constraints. The TSI-880 now replaces the need for these human observers under all weather conditions.
An onboard processor computes both fractional cloud cover and sunshine duration, storing the results and presenting data to users via an easy-to-use web browser interface. The self-contained design makes it well suited for mission-critical applications such as aviation and military meteorology monitoring. It captures images into standard JPEG files that are analyzed into fractional cloud cover; if networked via TCP/IP (10/100BaseT) or PPP (modem) it becomes a sky image server to remote any user via the web.
Specifications

Image Resolution: 352 x 288 color, 24-bit JPEG format
Sampling rate: Variable, with max of 30 sec
Operating Temperature: -40 C to +44 C
Weight/Size: Approx.70 lbs.(32 kg); dims: 20.83"x18.78"; height is 34.19"; mounts on 16.75x12" 1/4-20 bolt square
Power Requirements: 115/230 Vac; mirror heater duty cycle varies with air temperature: 560W with heater on / 60W off
Software: None required for immediate real time display; uses Internet Explorer or Netscape Browsers on MS-Windows, Mac, UNIX (an optional DVE/YESDAQ package is available for data archiving, display, MPEG day movie creation and data reprocessing)
Data Telemetry: LAN Ethernet (TCP/IP), telephone modem (PPP) or Data Storage Module option (for off grid sites)
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Precipitation:

TE525-L Specifications

  • Sensor Type: Tipping bucket/magnetic reed switch
  • Material: Anodized aluminum
  • Temperature: 0° to +50°C
  • Resolution: 1 tip
  • Volume per Tip: 0.16 fl. oz/tip (4.73 ml/tip)
  • Rainfall per Tip: 0.01 in. (0.254 mm)
  • Accuracy
    Up to 1 in./hr: ±1%
    1 to 2 in./hr: +0, -3%
    2 to 3 in./hr: +0, -5%
  • Funnel Collector Diameter:
    15.4 cm (6.06 in.)
  • Height: 24.1 cm (9.5 in.)
  • Tipping Bucket Weight:
    0.9 kg (2.0 lb)
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Station Pressure

CS105/CS105MD Barometric Pressure
Sensor
1. General
The CS105 analog barometer uses Vaisala’s Barocap silicon capacitive
pressure sensor. The Barocap sensor has been designed for accurate and stable
measurement of barometric pressure. The CS105 outputs a linear 0 to 2.5
VDC signal that corresponds to 600 to 1060 mb. It can be operated in a
powerup or continuous mode. In the powerup mode the datalogger switches
12 VDC power to the barometer during the measurement. The datalogger then
powers down the barometer between measurements to conserve power.
2. Specifications
Operating Range
Pressure: 600 mb to 1060 mb
Temperature: -40 C to +60 C
Humidity: non-condensing
Accuracy
Total Accuracy*** 0.5 mb @ +20 C
2 mb @ 0 C to +40 C
4 mb @ -20 C to +45 C
6 mb @ -40 C to +60 C
Linearity*: 0.45 mb @ 20 C
Hysteresis*: 0.05 mb @ 20 C
Repeatability*: 0.05 mb @ 20 C
Calibration uncertainty**: 0.15 mb @ 20 C
Long-Term Stability: 0.1 mb per year
* Defined as 2 standard deviation limits of end-point non-linearity,
hysteresis error, or repeatability error
** Defined as 2 standard deviation limits of inaccuracy of the working
standard at 1000 mb in comparison to international standards (NIST)
*** Defined as the root sum of the squares (RSS) of end-point non-linearity,
hysteresis error, repeatability error and calibration uncertainty at room
temperature


 

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