1. Status of requirements definition for the ACE multiangle, multispectral, polarimetric imager David J. Diner ACE workshop Salt Lake City, UT 6-7 November 2008

2. 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 capabilites cannot be established without impacting others.

3. SpecificationRationaleSource 3 kmAerosol measurements away from cloud edges ACOB white paper, §4.1 1 kmNot providedDecadal Survey 500 mImproved cloud edge discrimination and resolution of scene variability ACOB white paper, §1.2, 4.1 250 mStereo cloud-top and aerosol injection heights MISR experience 100 mCloud spatial heterogeneityACOB white paper, §2.2 SufficientRetrieve 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.

4. SpecificationRationaleSource 1500 km2-day coverage to overlap ocean color spectrometer ACE STM, v3a 400 kmFocus on process studiesACOB white paper, §2.2 SufficientCapture 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.

5. SpecificationConsensusNo consensus yet AnglesRange: 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) BandsUV-VNIR-SWIR coverageWavelength 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

6. 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