Experience learned and recommendations from AATSR Land Surface Temperature (and Emissivity)

Transcription

1 Experience learned and recommendations from AATSR Land Surface Temperature (and Emissivity) Gary Corlett 1, Darren Ghent 1, John Remedios 1, Philipp Schneider 2, Simon Hook 3 1 University of Leicester, 2 Nilu, 3 JPL

2 AATSR LST&E contributors David Llewellyn-Jones, John Remedios, Darren Ghent, Ed Comyn-Platt, Harjinder Sembhi, UoL Elizabeth Good, Met Office Hadley Centre Fred Prata, Philipp Schneider, NILU Andrew Birks, STFC RAL Claire Bulgin, Chris Merchant UoE Simon Hook and colleagues, JPL Jose Sobrino and colleagues, UoV Cesar Coll and colleagues, UoV Folke Olsen and Frank Goettsche, IMK Martin Wooster and colleagues, KCL Philippe Goryl, Paul Snoeij, ESA

3 LST&E validation Not as easy as SST But tractable Four main methods for LST&E validation Compare to in situ Radiance based Intercomparison Time series Multi-sensor approach is preferred Aids interpretation of results For AATSR Geolocation and view alignment more critical Limited use of 3.7 µm channel (poorly understood emissivity) for atmospheric correction

4 Validation of North American ASTER Emissivity Database (NAALSED) Hulley, G. C., Hook, S. J., and A.M. Baldridge, (2009), Validation of the North American ASTER Land Surface Emissivity Database (NAALSED) Version 2.0, Remote Sensing of Environment, 113,

5 KIT s 4 permanent LST&E validation stations Heitronics KT15.85 IIP radiometer Successful radiometer comparison at CEOS Proven homogeneity of sites > 100 km² Current validation of MSG-SEVIRI LST Well distributed on MSG-disk Temperate vegetation: Portugal, Evora Semi-arid (tiger bush): Senegal, Dahra Desert: Namibia, Gobabeb Kalahari bush: Namibia, Farms IR-radiometer Heitronics KT15.85 IIP chopped, precision radiometer: stability better than 0.12% per year narrow band 9.6μm -11.5μm (completely in atmospheric window) better than ±0.3K absolute accuracy 0.06K temperature resolution Full view angle: 8.5 One KT15 for each end-member One KT15 for sky radiance (reflected rad.) Campbell CR1000 logger sample at 1 min

6 LST&E Validation: In situ (Gobabeb) Day AATSR (operational) AATSR (UoL) Night SEVIRI (LandSAF) AATSR (operational) AATSR (UoL) SEVIRI (LandSAF)

7 LST&E Validation: Radiance based Coll, C., et al., Long-term accuracy assessment of land surface temperatures derived from the Advanced Along-Track Scanning Radiometer, Remote Sensing of Environment (2011), doi: /j.rse

8 LST&E Validation: Intercomparison Daytime LST differences between AATSR and SEVIRI (Jan and Jul 2006) Nighttime LST differences between AATSR and SEVIRI (Jan and Jul 2006)

9 LST&E Validation: Time series October 2005 December 2005 Time series analysis can be useful to identify artefacts in the product For example, cloud contamination in level-3 LST reported by C Kogler (ESA)

10 Lessons Learned: Negative Quickly identified major issues with AATSR LST product Took a while to resolve, but now unable to update product Scene identification (cloud masking, surface type) Cloud masking is an issue (particularly at night) Synergy with other sensors not fully exploited Must work at night (can t use visible channels) Must be dynamic Lots of national activities Very little international coordination Starting with CEOS WGCV LPV LST&E and IVOS groups

11 Possible LST&E Validation protocol Category Highest accuracy A B C D In situ A1 Radiancebased B1 Inter-comparison C1 Time series D1 A2 Accuracy Class A3 A4 B2 C2 D2 D3 A5 Lowest accuracy A6 B3 C3 D4

12 Lessons Learned: Positive Clear requirement for LST from users GlobTemperature workshop to assess this hp Dedicated experts; willingness to collaborate SST, LST, IST = ST Developments to auxiliary data giving improvements over the operational LST Other categories of validation increasingly being implemented and yielding new insights

13 Requirements: LST&E Sites Need very well characterised reference sites Traceable radiometers suitable for LST&E Measured surface emissivities; water vapour and aerosol measurements Uncertainty budget Build on existing heritage Tahoe, Salton Sea, Gobabeb, Evora etc. Carry out routine inter-comparisons of radiometers Investigate thermal pseudo-invariant sites Investigate air temperature network Night time only

14 Requirements: Cal/Val tools Multi-sensor match-up dataset In situ history where available (per site) Level 1b/1c data for multiple satellite sensors Auxiliary NWP data and forward model outputs Dummy locations (for sat/sat comparisons) Averaging tools BEAM

15 Recommendations Continue on from AATSR Need to improve cloud masking (particularly at night) Need agreed international validation protocols/procedures Improved international coordination of activities Project coordinator (akin to GHRSST) would be ideal Need to define site requirements with other agencies Very few high quality long-term reference sites exist we need more of them Need data sharing agreements Coordinate inter-comparisons with ship radiometers Need dedicated workshop(s) on LST validation Need more flexible processing of Level 2 Capability for rapid update and reprocessing