Observation Data

Platform Overview

WindBorne Systems has developed the Global Sounding Balloon (GSB), a long-duration controllable balloon-based observation platform optimized for repeated vertical profiling of the atmosphere. The GSB provides atmospheric observations of pressure, temperature, humidity, and wind speed and direction along its flight path. A single GSB flight is capable of remaining aloft for weeks or months and collecting dozens of vertical sounding profiles while traveling thousands of kilometers from the launch location.

What's Measured

The API returns the following variables for each observation data point. All values have passed automated quality control before reaching the API. Invalid data is excluded from the response.

API Field	Description	Unit
temperature	Ambient air temperature measured by a thermistor.	°C
humidity	Relative humidity at ambient air temperature measured by thin-film capacative sensors. Reported with respect to vapor pressure over liquid water above 0 °C, over ice below −23 °C, and interpolated between.	%
specific_humidity	Derived from relative humidity, temperature, and pressure measurements.	mg/kg
pressure	Barometric pressure measured by MEMS sensors.	hPa
altitude	Geopotential height relative to the EGM96 geoid, measured by multi-GNSS receiver.	meters
speed_u	East/west wind velocity component, eastward positive. Measured by multi-GNSS receiver.	m/s
speed_v	North/south wind velocity component, northward positive. Measured by multi-GNSS receiver.	m/s
latitude	Measured by multi-GNSS receiver.	degrees
longitude	Measured by multi-GNSS receiver.	degrees
timestamp	UTC measurement time.	unix timestamp

Data Pipeline & Latency

Measurements are recorded every 10 seconds on board the balloon. These are bundled into transmissions and downlinked via the Iridium satellite network. Server-side quality control runs automatically on receipt, after which the data is made available to the API.

Stage	Timing
On-board sampling interval	Every 10 seconds
Satellite downlink interval	typically 1–7 minutes (configurable)
End-to-end latency (measurement → API)	typically <15 minutes

Data Processing and Quality Control

All observations pass through automated quality control before appearing in the API. Data that did not pass quality control is excluded from the response. Data processing includes corrections for solar bias of the temperature sensor and temperature compensation and time lag correction of the humidity sensor. Average observation validity percentage for profiling data from 2024/7/1 through 2025/6/30 is shown below.

Variable	Acceptance while profiling
Altitude/Wind/Latitude/Longitude	99.7%
Pressure	98.4%
Temperature	88.8%
Humidity	77.7%

Sensor Performance

Sensor performance specifications are derived from in-lab testing and side-by-side launches, and validated through side-by-side radiosonde launches and intercomparison with ECMWF ERA5 reanalysis. Sensor performance meets or exceeds the most stringent WMO OSCAR 2.1 Global NWP requirements.

Parameter	Specification
Pressure, MEMS
Operating range	20 to 1050 hPa, −60 to 40 °C^a
Data resolution	0.03 hPa
Calibration uncertainty	0.2 hPa
Sounding reproducibility	0.25 hPa^b
Temperature, Thermistor
Operating range	−90 to 40 °C
Thermal time constant	τ₆₃ = 1 s in still air
Data resolution	0.3 °C
Calibration uncertainty	0.1 °C
Sounding reproducibility	0.25 °C^b
Humidity, E+E Elektronik
Operating range	0 to 100% RH
Response time	τ₆₃ = 0.9 s at 0 °C, 20 s at −40 °C
Data resolution	0.5% RH
Calibration uncertainty	2% RH
Sounding reproducibility	2.5% RH^b
Altitude, Multi-GNSS
Data resolution	8 m
Sounding reproducibility	3 m^c
Wind Speed, Multi-GNSS
Operating range	<\|100\| m/s onboard, ≥\|100\| m/s calculated ground-side
Data resolution	0.4 m/s
Sounding reproducibility	0.4 m/s^b

^a Main electronics, including pressure sensors, are always heated above −60 °C during flight
^b One standard deviation difference between simultaneously launched GSBs, matched at equivalent altitude
^c One standard deviation difference between simultaneously launched GSBs, matched at equivalent pressure
Humidity uncertainty specifications apply above −58 °C
All calibration uncertainties are quoted at 2σ

For full methodology and validation details, see Spisak et al. 2025.