Australian (IMOS) Contribu4on to SWOT Valida4on Christopher Watson 1,2 (cwatson@utas.edu.au), 1. Geography and Spa0al Sciences, University of Tasmania. 2. Integrated Marine Observing System Benoit Legresy 3,2 , Jack Beardsley 2 , 3. CSIRO Oceans and Atmosphere, Hobart, Australia. Arthur Zhou 1 , MaN King 1 Australian SWOT Working Group Workshop Bass Strait Valida4on Facility May 24, 2019 BoM, Sydney, Australia
Overview: The valida4on challenge: Nadir v Swath al4metry • Brief recap of the Bass Strait valida4on facility used • for nadir al4metry. Current plans for valida4on ac4vi4es as supported • by IMOS. Southern Ocean (SOFS) – Vongala – Bass Strait – AUSWOT Workshop /13 2 Australian Contribu>on to SWOT Cal/Val May 2019
The problem pre SWOT… Frame… …accurately and independently validate al0meter SSH ( SSH Alt ) Conceptually simple, but prac0cally, far more complex: Ionosphere… Ø Dynamic environment Ø Stringent accuracy requirements Ø Sustain observa4ons required Ø Many dependent variables Troposphere… Ø 𝑻𝑻𝑰↓𝑩 𝑻𝑻𝑰↓𝑩𝒎𝒖 𝒎𝒖 = spa4al integra4on within footprint, observed instantaneously Ø 𝑻𝑻𝑰↓𝑱 𝑻𝑻𝑰↓𝑱𝒐 𝑻𝒋𝒖𝒗 𝑻𝒋𝒖𝒗 = point measurement, o[en averaged in 4me 𝑻𝑻𝑰↓𝑱𝒐 𝑻𝒋𝒖𝒗 𝑻𝑻𝑰↓𝑱 𝑻𝒋𝒖𝒗 Various approaches to observe : Sea State… Ø Direct techniques at a offshore comparison point (CP) Ø Indirect techniques, derived at the coast, transformed to a CP Ø Rela4ve techniques (unable to resolve absolute datum) to assess temporal driN ( e.g. Mitchum, 2000, Ablain et al., 2009, Watson et al., 2015 ) Mul4ple missions… AUSWOT Workshop /13 3 Australian Contribu>on to SWOT Cal/Val May 2019
The problem pre SWOT… TOPEX / Poseidon Aug 1992 - Jason-1 Dec 2001 - So called ‘absolute’ valida4on takes a OSTM/Jason-2 geometric approach to the problem: June 2008 - Ø Valida0on presents a geode0c problem… Ø Observe SSH in situ in the same reference frame as the al0meter. Jason-3 Ø Pla[orm based GNSS (Harvest) Jan 2016 - Ø GNSS equipped buoys (Bass Strait and Corsica). Ø Tide gauges and BPRs. Sen4nel-3A Feb 2016 - Sen4nel-3B (Watson et al, 2004) Launching 25 Apr 2018 - AUSWOT Workshop /13 4 Australian Contribu>on to SWOT Cal/Val May 2019
Bass Strait, Australia: 1992-pres • Provides a southern hemisphere valida0on site ( White et al., 1994 ). • Comparison point ~25 km from land, ~50 m water depth. • Ini0ally an indirect approach via 0de gauge and geoid ( White et al., 1994 ), then moving to direct observa0on of SSH via moored oceanographic instruments and GPS equipped buoys ( Watson et al, 2003, 2004, 2010 etc ). • Sustained ongoing valida4on supported by IMOS , now extended to Sen0nel series al0meters, as well as into global TG assessments of bias driN (e.g. Watson et al., 2015). (Watson et al, 2011) 25 Years of Progress in Al>metry Watson et al. A review of 25 years of ongoing monitoring Azores Archipelago, Portugal
GNSS Buoys: • GNSS equipped buoys offer high temporal resolu0on, point sampling of SSH in the same reference frame as al0meters. • Standard devia0on of differences against SBE26+ BPR with dynamic ht correc0on typically < 2 cm. 25 Years of Progress in Al>metry 6 Watson et al. A review of 25 years of ongoing monitoring Azores Archipelago, Portugal
The new valida4on challenge with SWOT… Image: BRAT A network of GNSS buoys offers a geometric approach to valida0ng SWOT over < 100 km length scales – the exact sampling approach remains an open ques0on AUSWOT Workshop /13 7 Australian Contribu>on to SWOT Cal/Val May 2019
SWOT Fast Sampling Phase • Apart from cal/val, fast sampling phase presents opportuni0es for process studies… • IMOS supported cal/val focuses on Bass Strait, but with upgrades to SOTS and Yongala. Yongala mooring Bass Strait Cal/Val site SOFS AUSWOT Workshop /13 8 Australian Contribu>on to SWOT Cal/Val May 2019
SOFS (140°E, 47°S) • SOFS is one component of the Southern Ocean Time Series site in a highly energe0c region north of the ACC. • Posi0oned within SWOTs 1-day repeat swath. Rapizo et al., 2015 Rapizo et al., 2015 AUSWOT Workshop /13 9 Australian Contribu>on to SWOT Cal/Val May 2019
SOFS (140°E, 47°S) • Most recent deployment 17 March 2019. • SOFS surface expression augmented with a geode0c quality GNSS receiver and antenna as a trial deployment. • Iridium comms for heartbeat info, data logged internally. • Currently have 67+ days of observa0ons at 2 Hz. • Will soon commence some tests of remote reconfigura0on (changing sampling to preserve memory etc). • Service visit ~March 2020 will retrieve/redeploy new. • Processing will yield high accuracy SSH and wave data (complemen4ng exis4ng wave sensors) . • Correc0on of heave and 0lt likely to be problema0c. AUSWOT Workshop /13 10 Australian Contribu>on to SWOT Cal/Val May 2019
Yongala (147°E, 19°S) Yongala mooring (~26 m water depth) is part of the IMOS supported na0onal mooring array. Sits • within the 1-day fast sampling orbit. Surface expression of the mooring to be augmented with geode0c GNSS receiver. Poten0al • deployment of addi0onal 5 beam ADCP. AUSWOT Workshop /13 11 Australian Contribu>on to SWOT Cal/Val May 2019
Bass Strait Bass Strait infrastructure (in partnership with interna0onal collaborators) to include ~12 • GNSS buoys to deliver SSH at 2 Hz (near real 0me). P / T / S moorings at exis0ng comparison points. • Addi0onal 5 beam ADCP deployments. • High resolu0on modelling ac0vity (CSIRO SHOC) • STLY (GPS) RKCP (GPS) BUR2 (TG+GPS) 40 km AUSWOT Workshop /13 12 Australian Contribu>on to SWOT Cal/Val May 2019
Why Bass Strait? • Bass Strait offers a complementary cal/val target to augment planned ac4vi4es off the Californian coast and in the Mediterranean. • Oceanographically benign (SWH < 2 m), STLY (GPS) dominant signal will be 4dal (predictable). RKCP (GPS) • Accessible / reconfigurable / compara4vely BUR2 (TG+GPS) inexpensive. 40 km • Near real 4me poten4al. • Exact deployment configura4on TBD (cal/val workshop June 2019) AUSWOT Workshop /13 13 Australian Contribu>on to SWOT Cal/Val May 2019
Bass Strait Instrumenta4on New Mk-V GNSS buoy construc0on finally underway (x2): Custom design, fabricated largely from welded polypropylene. • Payload includes GNSS+INS (Xeos Resolute GNSS, XSENS INS, waterproof • ~1.2 m Javad antenna) and SST (Seabird SBE56) sensors. Solar power system. • Cellular telemetry, iridium tracking. • ~60 kg deployment weight • Low cost (US$15-20K ex GNSS) • Aimed at deployment dura0ons of ~1-2 months. • First deployment ~June 2019. • XEOS Resolute GNSS receiver (Septentrio board) XSENS INS to aid pla[orm orienta0on and posi0oning AUSWOT Workshop /13 14 Australian Contribu>on to SWOT Cal/Val May 2019
Studies underway AUSWOT Workshop /13 15 Australian Contribu>on to SWOT Cal/Val May 2019
Summary In situ valida4on of satellite al4metry represents a Observa4ons (increasingly) complex task: • Orbit + range + correc0ons • Engineering calibra0ons Ø Inherently mul0-disciplinary, mul0-faceted: geodesy / oceanography / geophysics / engineering. Ø Working at the ~1 cm level is challenging. Data Genera4on Bass Strait contribu4ons: • ‘GDR’ Produc0on chain Ø Purely geometric approach to valida0on Ø Well instrumented, well understood region Ø Further work required to design deployment configura0on ‘Calibra4on’ ‘Valida4on’ SOFS / Vongala contribu4ons: • Algorithm development • Whole of system product valida0on via in • Technical adjustments situ sites and rela0ve strategies Ø GNSS addi0ons will further supplement data from these • Many other QA/QC analyses by project sites. teams AUSWOT Workshop /13 16 Australian Contribu>on to SWOT Cal/Val May 2019
Ques4ons? Christopher Watson 1,2 (cwatson@utas.edu.au), 1. Geography and Spa0al Sciences, University of Tasmania. 2. Integrated Marine Observing System Benoit Legresy 3,2 , Jack Beardsley 2 , 3. CSIRO Oceans and Atmosphere, Hobart, Australia. Arthur Zhou 1 , MaN King 1 Australian SWOT Working Group Workshop Bass Strait Valida4on Facility May 24, 2019 BoM, Sydney, Australia
Spares AUSWOT Workshop /13 18 Australian Contribu>on to SWOT Cal/Val May 2019
Spares Chelton (2019) AUSWOT Workshop /13 19 Australian Contribu>on to SWOT Cal/Val May 2019
Chelton (2019) AUSWOT Workshop /13 20 Australian Contribu>on to SWOT Cal/Val May 2019
SWOT Fast Sampling Phase Yongala mooring Bass Strait SOTS Cal/Val site Kerg. Is. ACC AUSWOT Workshop /13 21 Australian Contribu>on to SWOT Cal/Val May 2019
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