Campaigns are an important part of the validation of the SKIM concept, with two important objectives
- demonstrating the sensitivity of the measured signal (frequency Doppler on the radar) to the geophysical parameters (currents and waves)
- validating the "End to End" simulation tools. It is the simulator that will generalize the conditions observed in the campaign to the real instrument on the satellite and the wide range of conditions that will be observed during the mission lifetime.
For SKIM we are using data from past campaigns both from platforms at sea (e.g. Yurovsky et al. 2016, 2018) and airborne systems.
In particular we have used Ka-band radar systems such as AirSWOT (Nouguier et al. 2018). This system is a SAR system and we know that the Doppler centroid phase of a pulse-pair system like SKIM is equivalent to the Doppler centroid estimated from Single Look Complex SAR images from AirSWOT. A great success of these campaigns was the detailed validation of the wave contribution to the measure velocity, and its dependance on the incidence angle.
Malingre issues, form the objective of the upcoming DRIFT4SKIM capaign:
- actually demonstrating the measurements with a pulse-pair method
- characterize the environmental conditions in details (currents, winds and waves)
- investigating the relation of the surface velocity to a depth-varying current and waves
- linking the estimated current velocity to reference current measurements : drifters , ADCPs, HF radars
The campaign will take place off the French coast near Brest, with particular focus in two "boxes" with uniform currents (box 2) and strongly varying current (box 1). This region is covered by HF radars operated by SHOM. The date of the campaign is set to November 2018, driven by the availability of the aircrafts from SAFIRE, the French research aircraft operator.
KuROS on ATR42
The main instruments to be deployed are the KuROS radar (Doppler pulse-pair Ku-band system with a rotating antenna, developed by LATMOS and CNES), it will be deployed on the SAFIRE ATR42 plane. KuROS has been operated on the ATR42 in several campaigns in preparation for wave spectra measurements by the SWIM instrument on CFOSAT, with also some preliminary analysis of the Doppler signal (Caudal et al. 2014).
The KuROS instrument has 2 antennas and we will mostly work with the one around 14° incidence, similar to the 12° outer beams of SKIM. For wave measurements the principle of KuROS is similar to SWIM and SKIM, with a rotation of a radar antenna that allows to measure the waves of different wavelengths that propagate in the look direction, toward and away from the radar. For current measurements we will also fly with the antenna in a fixed azimuth and fly over the same "boxes" with different flight direction relative to the current, to make sure that we really understand the contribution of waves and currents.
"Ground truth": drifters
Velocity measurements with drifter is a proven technology and the most used type of drifter are those used in the "Surface Velocity Program" (SVP).