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Non-satellite instrument techniques involved
Radiosonde
Ozonesonde
Lidar
FPH/CFH
Gap remedies
Related gaps
G6.01 Dispersed governance of high-quality measurement assets leading to gaps and redundancies in capabilities and methodological distinctions
G6.06 Provision of reference-quality measurements where technically feasible on a continuous basis, to maximise opportunities for the validation of satellite and derived products
Detailed description

For some non-satellite instruments, there are geophysical limitations as to when measurements can be undertaken, e.g. an FTIR requires direct line of sight to the sun or a MAX-DOAS can only measure at sunrise/sunset.

Other instruments can and do operate 24/7 and therefore could always capture a co-location, if the satellite passes overhead. For example, both GNSS-PW and microwave radiometers, in principle, operate on a 24/7 basis. G6.06 discusses issues around their continuous operation where this is not yet assured.

But for many non-satellite measurement techniques, it is for financial or logistical reasons that measurements are solely episodic. For example, operational radiosonde launches tend to be twice-daily or at best four times daily at fixed local times. Similarly, for many instrument configurations, lidar operations may be made only when staff are available. These types of considerations effect very many non-satellite measurements, which could, in principle, be better targeted to support EO-sensor characterization by taking measurements much closer to satellite-overpass time. This would reduce the co-location mismatch and thus the attendant mismatch uncertainties. Because funding for these observations typically is not concerned with satellite characterisation, the current sampling strategy ends up being sub-optimal for satellite characterisation. Better aligning sampling strategies with times of satellite overpass, which are predictable a substantial time in advance, would increase their utility to satellite Cal/Val activities. 

Operational space missions or space instruments impacted
Independent of specific space mission or space instruments
Validation aspects addressed
Radiance (Level 1 product)
Geophysical product (Level 2 product)
Time series and trends
Representativity (spatial, temporal)
Calibration (relative, absolute)
Auxiliary parameters (clouds, lightpath, surface albedo, emissivity)
Gap status after GAIA-CLIM
After GAIA-CLIM this gap remains unaddressed
Dependencies

G6.01 - To be addressed with G6.03

Argument: The resolution to the current gap will be simpler if a more unified governance of non-satellite measurement networks is achieved and the data is provided from these networks in a more unified manner.

G6.06 To be addressed with G6.03

Argument: Operationalising instruments that can be operated 24/7 removes the current gap for the instruments affected. 

References
  • Tradowsky J S, C P Burrows, S B Healy and J Eyre, 2017: A new method to correct radiosonde temperature biases using radio occultation data. J. Appl. Meteor. Climatol., 56, 1643-1661, https://doi.org/10.1175/JAMC-D-16-0136.1

There are many non-satellite measurement systems that, in principle, could be used for the purposes of satellite characterisation on a sustained basis. Such measurements are metrologically well characterised and understood. They often measure variables, which are measured or measurable from space. However, many of the measurement systems are discontinuous (discrete) in time and their measurement scheduling is typically made with no regard to satellite-overpass times. This considerably diminishes their value for satellite Cal/Val activities. Better scheduling would increase their intrinsic value for satellite programs.