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Class 1 · 100 m
Class 2 · 30 m
Class 3 · 10 m
Class 4 · 3 m
24 m · class 3
0 min
60 min
120 min
180 min
-10 °C
0 °C
10 °C
20 °C
30 °C
Logger · 1-min air temperature
76 flagged
SI kelvin · ITS-90
National metrology institute
Accredited laboratory
Field reference
Station sensor
U 0.040 °C
U 0.057 °C
U 0.101 °C
1 · Observed variable
2 · Purpose of observation
3 · Station/platform
4 · Environment
5 · Instruments and methods
6 · Sampling
7 · Data processing and reporting
8 · Data quality
9 · Ownership and data policy
10 · Contact
0 km
50 km
100 km
150 km
200 km
5 km
10 km
15 km
0.5° · 1.5 km
P
S
30 s · 100 sps
0 dbar
1,000 dbar
2,000 dbar
Ascent · 5.5 h
Drift · 10 day cycle
Class 1 · 100 m; Class 2 · 30 m; Class 3 · 10 m; Class 4 · 3 m
Sensors · Explainer
Interactive
An observation carries where it was made, how it was checked, what it traces back to and who can vouch for it. Seven steps from a weather station’s mast to a float two kilometres down.
01 · Siting
WMO-No. 8
WMO-No. 8 grades a site from class 1 to 5 for each variable. For air temperature it is the distance to heat sources such as buildings, car parks and water: class 1 beyond 100 m, then 30, 10 and 3 m. For wind it is distance in obstacle heights: 30, 10, 5 and 2.5 times. Classes 3 to 5 add up to 1, 2 and 5 °C of uncertainty to temperature.
Variable
02 · Quality control
Flags
The sensor feeds a logger that averages one-minute values; automatic checks flag each one before it travels. The range check rejects air temperatures outside −80 to +60 °C, the step check doubts a jump of more than 3 °C in a minute, and the persistence check doubts an hour that varies by less than 0.1 °C. Inject a fault and watch the flags.
Faults
03 · Traceability
GUM
Each calibration compares an instrument with a better one and adds its own uncertainty. Following the GUM, independent standard uncertainties combine as uc = √Σu², and the expanded uncertainty U = 2uc covers about 95 %. A display that reads in 0.1 °C steps alone contributes 0.1/√12. WMO-No. 8 asks for 0.1 K on air temperature.
Display resolution
Expanded uncertainty down the chain, k = 2
Lab reference
0.040 °C
+ bath
0.057 °C
Station sensor
0.101 °C
WMO-No. 8 target
0.100 °C
04 · WIGOS metadata
WMO-No. 1192
The WIGOS Metadata Standard describes an observation in ten categories, and a WIGOS station identifier names the station worldwide: series, issuer, issue number and local identifier, as 0-20000-0-71xxx for a station with a WMO number. Fill the categories this station reports.
Categories reported
Issuer of identifier
05 · Radar volume scan
VCP
A weather radar sweeps a stack of elevation angles every few minutes. Under standard refraction the beam rides an Earth of 4/3 its radius: h = √(r² + (kea)² + 2rkea sin θ) − kea. Far from the radar, the lowest tilt overshoots the weather near the ground and the beam widens as r·θ. Heights are stretched tenfold.
Radar
06 · Seismic vault
GNSS time
The P wave outruns the S wave, about 6 against 3.5 km/s in the crust, so the gap between them grows with distance: S − P = R(1/Vs − 1/Vp), about 8.4 km per second of gap. A GNSS receiver on the vault stamps every sample; any clock error moves the event by Vp × error.
Clock error
Samples per second
07 · Ocean profile
Argo
A profiling float changes its buoyancy with an oil bladder: it sinks to drift at 1,000 dbar, drops to its profile depth, then rises sampling temperature, salinity and pressure, and sends the profile by satellite before it sinks again. A decibar of pressure is close to a metre of depth.
Sample every
Cycle
An observation carries where it was made, how it was checked, what it traces back to and who can vouch for it. Seven steps from a weather station’s mast to a float two kilometres down.
WMO-No. 8 grades a site from class 1 to 5 for each variable. For air temperature it is the distance to heat sources such as buildings, car parks and water: class 1 beyond 100 m, then 30, 10 and 3 m. For wind it is distance in obstacle heights: 30, 10, 5 and 2.5 times. Classes 3 to 5 add up to 1, 2 and 5 °C of uncertainty to temperature.
The sensor feeds a logger that averages one-minute values; automatic checks flag each one before it travels. The range check rejects air temperatures outside −80 to +60 °C, the step check doubts a jump of more than 3 °C in a minute, and the persistence check doubts an hour that varies by less than 0.1 °C. Inject a fault and watch the flags.
Each calibration compares an instrument with a better one and adds its own uncertainty. Following the GUM, independent standard uncertainties combine as uc = √Σu², and the expanded uncertainty U = 2uc covers about 95 %. A display that reads in 0.1 °C steps alone contributes 0.1/√12. WMO-No. 8 asks for 0.1 K on air temperature.
The WIGOS Metadata Standard describes an observation in ten categories, and a WIGOS station identifier names the station worldwide: series, issuer, issue number and local identifier, as 0-20000-0-71xxx for a station with a WMO number. Fill the categories this station reports.
A weather radar sweeps a stack of elevation angles every few minutes. Under standard refraction the beam rides an Earth of 4/3 its radius: h = √(r² + (kea)² + 2rkea sin θ) − kea. Far from the radar, the lowest tilt overshoots the weather near the ground and the beam widens as r·θ. Heights are stretched tenfold.
The P wave outruns the S wave, about 6 against 3.5 km/s in the crust, so the gap between them grows with distance: S − P = R(1/Vs − 1/Vp), about 8.4 km per second of gap. A GNSS receiver on the vault stamps every sample; any clock error moves the event by Vp × error.
A profiling float changes its buoyancy with an oil bladder: it sinks to drift at 1,000 dbar, drops to its profile depth, then rises sampling temperature, salinity and pressure, and sends the profile by satellite before it sinks again. A decibar of pressure is close to a metre of depth.
The smallest unit is one station, sited to a known class. A site places several instruments around shared power and a clock; a cluster shares a calibration bench and a travelling reference; a region runs one network with one metadata practice; the global layer is many operators’ networks made comparable. The WMO Integrated Global Observing System is the framework that lets observations from different owners be used together.
Sources WMO-No. 1160, Manual on the WMO Integrated Global Observing System
An observation is checked, encoded in a standard format and published once. In the WMO Information System 2.0, centres publish notifications through message brokers using MQTT, users subscribe and download over the web, and a global discovery catalogue describes every dataset. A value that fails quality control is flagged or held back, so a subscriber receives data together with its quality, not raw readings alone.
Sources WMO-No. 1060, Manual on the WMO Information System, including WIS 2.0
Every sensor drifts. A network keeps them honest with routine field checks against a travelling reference, recalibration on a schedule and replacement in rotation. Comparing each station with its neighbours flags the one whose readings wander, so the next visit goes where it is needed rather than on a fixed round. The WMO guide sets out inspection and calibration practice for each kind of instrument.
Sources WMO-No. 8, Guide to Instruments and Methods of Observation
A station lives through a site survey, installation, calibration, years of operation and, often, a move or a new sensor. Each change can put a step into a long record. The climate monitoring principles ask that changes be assessed before they are made and that old and new systems overlap for a while; homogenisation methods then detect and adjust the breaks that remain.
Sources GCOS Climate Monitoring Principles; WMO-No. 1245, Guidelines on Homogenization
Which siting class does each station meet, and where is that written down? Can every value be traced to a calibration record? Is the metadata complete enough for someone else to use the data years from now? Under which data policy is it shared? The WMO unified data policy separates core data, exchanged free and without restriction, from recommended data that may carry conditions.
Sources WMO Unified Data Policy, Resolution 1 of the Extraordinary Session of the World Meteorological Congress