# Presentation: 664392

## Development of the second-generation ‘operational’ algorithm

## The Satellite Signal is complicated

**Assumptions**
- Aerosol physics: scattering/extinction properties
- Radiative Transfer (including Rayleigh and wavelength)
- Surface Properties
- Retrieval Technique

- (not to mention:
-  cloud effects, calibration, etc)

## Aerosol physics(e.g. assuming aerosol scattering/extinction properties)

## Aerosol optical models

- New Aerosol models improve retrievals for CLAMS and SAFARI
- Suggests need to re-evaluate models, globally

- Revised size distribution for CLAMS (Levy et al., 2005)

- Revised SSA for SAFARI (Ichoku et al., 2002)

## Global aerosol optical models An AERONET view (since 1994)

- 0 ~ 0.91,0.85,0.95

- Global aerosol optical models An AERONET view (since 1994)

- 0 ~ 0.85, 0.91, 0.95 (Fine)
- 0 ~ 0.95 (Coarse/Spheroid/Dust)

- Absorbing

- JJA

- Cluster by 0 and g, seasonal, ---> 3 fine-dominated models

- Non-absorbing

- Moderate absorbing

## Radiative Transfer and lookup tables (and Rayleigh and wavelengths)

- Re-calculated ‘central’ MODIS wavelength for each channel. (Combination of MODIS response function and spectral dependence of F0). Corrected assumed sea-level spectral Rayleigh optical depth.
- Calculated TOA reflectance and atmospheric transmission functions for lookup tables, for a variety of aerosol loadings and geometry
- Radiative Transfer code includes atmospheric polarization effect on TOA reflectance (up to 10% error if neglected; Levy et al., 2004)

## Surface Reflectance Properties

## Surface reflectance ratios (CLAMS-2001) “Atmospheric Correction”surface = MODIS - AERONET

- Reduces ocean/land discontinuity

- But over-corrects here

- C004

- s0.47** **/ s2.1 = 0.25
- s0.66** **/ s2.1 = 0.50

- Constant ratios do not work everywhere!! (Levy et al., 2005)

- CLAMS-derived

- s0.47** **/ s2.1 = 0.37
- s0.66** **/ s2.1 = 0.63

-  = 0.08

## Surface reflectance: global

- 550 < 0.2: N = 4200

- VIS vs IR

- Blue vs Red

- y = 0.011 + 0.259x, R = 0.75
- y = 0.001 + 0.551x, R = 0.93

- y = -0.008 + 0.508x, R = 0.87

- C005 (parameterization of 2.1 m, angle, and surface)
- s0.66** **= f0.66(s2.1, NDVISWIR)
- s0.47** **= g0.47(s0.66, NDVISWIR)

- C004 (Global fixed ratio of VIS to 2.1 m)
- s0.66** **= 0.5(s2.1); s0.47** **= 0.25(s2.1)

## Inversion of Spectral Reflectance

## Retrieval technique

**NEW (c005)**
- Aerosol information at 2.1 m
- Inversion of 3channels yields  (fine aerosol weighting) and s (surface reflectance)
- Retrieved at 0.55 m

- Spectral reflectance of different aerosol

**OLD (c004)**
- No aerosol at 2.1 m
- 2.1 for surface only
- Independent retrievals at 0.47 and 0.66 m
- Interpolated to 0.55 m

## Retrieval: The Inversion

- Coarse

- Fine

- Radius (μm)

- wavelength

- reflectance

- Calculate amount and weighting of fine-dominated model (to total ), combined with the surface reflectance s, that best matches the observed spectral reflectance (0.47, 0.66 and 2.1m)

- Stolen from L. Remer

- coarse

- surface

- fine

- combo

- 0.55 m

## Summary of c005 improvements

-  Recomputed center wavelengths and Rayleigh OD
-  Lookup Table includes atmospheric polarization for intensity
-  Aerosol models based on AERONET Dubovik retrievals and new geographic distribution
-  Surface reflectance relationships are functions of vegetation index and scattering angle
-  New inversion algorithm implemented
-  Valid range of  extended to -0.05
-  Subpixel snow mask implemented
-  Cloud mask adjusted
-  Column mass concentration product corrected units
-  New products and new Quality Assurance logic

- New physics, Algorithmic details, other people’s work

## Results

## Sanity Check: Images   over US East Coast

- C005: more continuity from land to ocean

- August 4, 2006

- C004

- C005

- Anthony Wimmers, CIMMS

- 0.0           0.2           0.4           0.6         0.8         1.0

- Cold front

## Validation: Out-sourcing to India

- Kanpur is an industrial city located in the *Indo-Gangetic Basin, *surrounded by tall Himalaya in the north and mountains of height about 500-1000m in the south

- C004

- C005

- Aqua: 2002-2005

- R=0.82; 68%

- R=0.64; 59%

- Hiren Jethva: PhD student at Indian Institute for Science