Abstract
Among the various challenges that spaceborne radar observations of the face, the following two issues are probably of a higher priority: inadequate dynamic resolution, and ineffective vertical penetration. It is therefore the vision of the National Laboratory for Marine Science and Technology of China that two highly anticipated breakthroughs in the coming decade are likely to be associated with radar interferometry and lidar (OL) technology, which are expected to make a substantial contribution to a submesoscale-resolving and depth-resolving observation of the ocean. As an expanded follow-up of SWOT and an oceanic counterpart of CALIPSO, the planned Guanlan science mission comprises a dual-frequency (Ku and Ka) interferometric altimetry (IA), and a near-nadir pointing OL. Such an unprecedented combination of sensor systems has at least three prominent advantages. (i) The dual-frequency IA ensures a wider swath and a shorter repeat cycle which leads to a significantly improved temporal and spatial resolution up to days and kilometers. (ii) The first spaceborne active OL ensures a deeper penetration depth and an all-time detection which leads to a layered characterization of the optical properties of the subsurface ocean, while also serving as a near-nadir altimeter measuring vertical velocities associated with the divergence, and convergence of geostrophic eddy motions in the mixed layer. (iii) The simultaneous functioning of the IA/OL system allows for an enhanced correction of the contamination effects of the atmosphere and the air-sea interface, which in turn considerably reduces the error budgets of the two sensors. As a result, the integrated IA/OL payload is expected to resolve the variability at submeso and sub-week scales with a centimeter-level accuracy, while also partially revealing marine life systems and ecosystems with a 10-m vertical interval in the euphotic layer, moving a significant step forward toward a transparent ocean down to the vicinity of the thermocline, both dynamically and bio-optically.
Highlights
Since the advent of ocean radar satellite in the 1970s (Fu et al, 2010), its development has followed three generic trends: (i) better sampling, (ii) higher accuracy, and (iii) more variables
In order to optimize the performance of each payload onboard the Guanlan satellite, two potential science orbits are proposed with a possible mid-term maneuver in between (Table 2): A low orbit of 495.953 km which is ideal for the ocean lidar (OL) to maximize its vertical penetration, and a high orbit of 791.254 km which is necessary for the interferometric altimeter (IA) to ensure a wide swath and fine spatiotemporal resolution
The centimeter-level precise orbit determination (POD) of the Guanlan satellite relies on the combination of the Beidou/GPS-based global navigation satellite system (GNSS) and the satellite laser ranging (SLR) system, where the multimode GNSS receiver is used for orbit tracking, the onboard SLR is used for calibrating orbit error, and a multifrequency scheme is applied for eliminating ionospheric errors in the observation data
Summary
Since the advent of ocean radar satellite in the 1970s (Fu et al, 2010), its development has followed three generic trends: (i) better sampling, (ii) higher accuracy, and (iii) more variables. The ultimate goal of ocean remote sensing is toward a quantitative derivation of all required variables, with a satisfactory accuracy, and a perfect sampling in near-real time. In reality, this can never be fully realized, but can always be gradually approached. This can never be fully realized, but can always be gradually approached In this white paper, the concept design of the Chinese Guanlan science mission with an interferometric altimeter (IA) and an ocean lidar (OL) onboard is described. We will demonstrate that the IA payload is expected to make a significant contribution to satellite altimetry in aspects of the above-mentioned trends (i) and (ii), while the OL payload is a good example of expanding remote sensing capacity in aspects of those trends mentioned in (i) and (iii)
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