Australian (IMOS) Contribu4on to SWOT Valida4on Christopher Watson - - PowerPoint PPT Presentation

Australian (IMOS) Contribu4on to SWOT Valida4on

Australian SWOT Working Group Workshop

May 24, 2019 BoM, Sydney, Australia

1. Geography and Spa0al Sciences, University of Tasmania. 2. Integrated Marine Observing System 3. CSIRO Oceans and Atmosphere, Hobart, Australia.

Christopher Watson1,2 (cwatson@utas.edu.au), Benoit Legresy3,2, Jack Beardsley2, Arthur Zhou1, MaN King1

Bass Strait Valida4on Facility

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

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

2

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

The problem pre SWOT…

3

…accurately and independently validate al0meter SSH (SSHAlt) Various approaches to observe :

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)

​𝑻𝑻𝑰↓𝑱 𝑻𝑻𝑰↓𝑱𝒐 𝑻𝒋𝒖𝒗 𝑻𝒋𝒖𝒗

Conceptually simple, but prac0cally, far more complex:

Ø Dynamic environment Ø Stringent accuracy requirements Ø Sustain observa4ons required Ø Many dependent variables Ø Ø

spa4al integra4on within footprint, observed instantaneously

​𝑻𝑻𝑰↓𝑩 𝑻𝑻𝑰↓𝑩𝒎𝒖 𝒎𝒖 =

point measurement, o[en averaged in 4me

​𝑻𝑻𝑰↓𝑱 𝑻𝑻𝑰↓𝑱𝒐 𝑻𝒋𝒖𝒗 𝑻𝒋𝒖𝒗 =

Frame… Ionosphere… Troposphere… Sea State… Mul4ple missions…

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

The problem pre SWOT…

4

(Watson et al, 2004)

TOPEX / Poseidon Aug 1992 - Jason-1 Dec 2001 - OSTM/Jason-2 June 2008 - Jason-3 Jan 2016 - Sen4nel-3A Feb 2016 - Sen4nel-3B Launching 25 Apr 2018 -

So called ‘absolute’ valida4on takes a geometric approach to the problem:

Ø Valida0on presents a geode0c problem… Ø Observe SSHin situ in the same reference frame as the al0meter. Ø Pla[orm based GNSS (Harvest) Ø GNSS equipped buoys (Bass Strait and Corsica). Ø Tide gauges and BPRs.

25 Years of Progress in Al>metry

Azores Archipelago, Portugal

Watson et al. A review of 25 years of ongoing monitoring

Bass Strait, Australia: 1992-pres

(Watson et al, 2011)

• 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).

25 Years of Progress in Al>metry

Azores Archipelago, Portugal

Watson et al. A review of 25 years of ongoing monitoring

GNSS Buoys:

6

• 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.

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

The new valida4on challenge with SWOT…

7

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

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

SWOT Fast Sampling Phase

8

• 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 SOFS Bass Strait Cal/Val site

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

SOFS (140°E, 47°S)

9

Rapizo et al., 2015 Rapizo et al., 2015

• 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.

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

SOFS (140°E, 47°S)

10

• 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.

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Yongala (147°E, 19°S)

11

• 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.

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Bass Strait

12

STLY (GPS) RKCP (GPS) BUR2 (TG+GPS)

40 km

• 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)

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Why Bass Strait?

13

40 km

• 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),

dominant signal will be 4dal (predictable).

• Accessible / reconfigurable / compara4vely

inexpensive.

• Near real 4me poten4al.
• Exact deployment configura4on TBD (cal/val

workshop June 2019)

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Bass Strait Instrumenta4on

14

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

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.

~1.2 m

XEOS Resolute GNSS receiver (Septentrio board) XSENS INS to aid pla[orm

• rienta0on and

posi0oning

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

15

Studies underway

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Summary

16

Observa4ons

• Orbit + range + correc0ons
• Engineering calibra0ons

‘Valida4on’

• Whole of system product valida0on via in

situ sites and rela0ve strategies

• Many other QA/QC analyses by project

teams

‘Calibra4on’

• Algorithm development
• Technical adjustments

Data Genera4on

• ‘GDR’ Produc0on chain

In situ valida4on of satellite al4metry represents a (increasingly) complex task:

Ø Inherently mul0-disciplinary, mul0-faceted: geodesy /

• ceanography / geophysics / engineering.

Ø Working at the ~1 cm level is challenging.

Bass Strait contribu4ons:

Ø Purely geometric approach to valida0on Ø Well instrumented, well understood region Ø Further work required to design deployment configura0on

SOFS / Vongala contribu4ons:

Ø GNSS addi0ons will further supplement data from these sites.

Ques4ons?

Australian SWOT Working Group Workshop

May 24, 2019 BoM, Sydney, Australia

1. Geography and Spa0al Sciences, University of Tasmania. 2. Integrated Marine Observing System 3. CSIRO Oceans and Atmosphere, Hobart, Australia.

Christopher Watson1,2 (cwatson@utas.edu.au), Benoit Legresy3,2, Jack Beardsley2, Arthur Zhou1, MaN King1

Bass Strait Valida4on Facility

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Spares

18

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

Spares

19 Chelton (2019)

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

20 Chelton (2019)

/13

AUSWOT Workshop May 2019

Australian Contribu>on to SWOT Cal/Val

SWOT Fast Sampling Phase

21 Yongala mooring SOTS Bass Strait Cal/Val site ACC

• Kerg. Is.