Status of requirements definition for the ACEmultiangle, multispectral, polarimetric imager

David J. Diner

ACE workshopSalt Lake City, UT

6-7 November 2008

Top level requirements

Specification

Horizontal spatial resolution

Swath width

Number of angles and angular range

Spectral bands, spectral range, and number with polarization capability

Polarization uncertainty

A systems view is necessary, as certain capabilitescannot be established without impacting others.

Specification Rationale Source

3 km Aerosol measurements away from cloud edges

ACOB white paper, §4.1

1 km Not provided Decadal Survey

500 m Improved cloud edge discrimination and resolution of scene variability

ACOB white paper, §1.2, 4.1

250 m Stereo cloud-top and aerosol injection heights

MISR experience

100 m Cloud spatial heterogeneity ACOB white paper, §2.2

Sufficient Retrieve aerosols in heterogeneous conditions

ACE STM, v3a

Range of opinions on horizontal spatial resolution

Comments:• Different channels may have different requirements. • Cloud 3D effects on aerosol retrievals need to be addressed.

Specification Rationale Source

1500 km 2-day coverage to overlap ocean color spectrometer

ACE STM, v3a

400 km Focus on process studies ACOB white paper, §2.2

Sufficient Capture aerosol events in monthly mean statistics at global model grid resolutions

ACE STM, v3a

Range of opinions on swath width

Comments:• Capabilities overlapping the lidar/radar views may differ from those within the broader swath. • Establishing role of atmospheric instruments in ocean color measurement will help resolve swath requirement.

Specification Consensus No consensus yet

Angles Range: Nadir to oblique (60º-70º) along-track

Number:

<10 to capture general scattering/polarization phase function shape; separate aerosol from surface; stereo; vs.

>15 to do above plus >60 to resolve detailed angular features (e.g., cloudbow)

Bands UV-VNIR-SWIR coverage Wavelength of shortest band (355 vs. 380 nm)

Number and spectral range of polarization bands

Polarization uncertainty

Better than 2% required for aerosols

0.1% vs. 0.5% vs. 1.0%

Range of opinions on other requirements

Paths to resolving requirements

An airborne ACE simulator capability is critical• RSP, AirMSPI, HSRL collocated on ER-2 for aerosols• PACS on ER-2 if possible, or WB-57 (easier accommodation)• Additional synergistic instruments must be identified • Simultaneous ground and in situ data required

Radiative transfer simulations are also critical• Documentation of sensitivity studies (along with key assumptions) needed

These activities require substantive funding by NASA HQ• Need to identify, capture results of, and possibly repurpose already funded efforts• New efforts specifically targeted at resolving areas of disagreement on instrument requirements are essential