Shaima Nasiri University of Wisconsin-Madison Bryan Baum NASA - Langley Research Center Detection of Overlapping Clouds with MODIS: TX-2002 MODIS Atmospheres Retreat St. Michael’s, Maryland 18 March, 2003

Improve MODIS satellite cloud property retrievals by: Developing a technique to detect thin cirrus overlying opaque water clouds Applying the technique globally Estimating errors in optical thickness and effective radius retrievals due to single layer cloud assumption Demonstrate technique using MODIS data from TX-2002 experiment Goals

TX-2002: 11 Dec., 2002 ER-2 flight track overlaid on GOES-8 IR window image San Antonio 19:16 underflight of MODIS

TX-2002: 11 Dec., 2002 MODIS band 31 (11 µm) Aqua 11 µm brightness temperature. Yellow circle marks ER-2 underflight location at 1916 UTC

MODIS µm Reflectance Louisiana N During TX-2002 Field Exeriment Aqua Overpass (circle is at 1916 UTC) Over Gulf of Mexico South of Louisiana

MODIS - 11 µm Brightness Temperature Louisiana N During TX-2002 Field Exeriment Aqua Overpass (circle is at 1916 UTC) Over Gulf of Mexico South of Louisiana

Color Mapping 0.65 µm R --> Red 2.13 µm R --> Green 11 µm BT (flipped) --> Blue Ice clouds appear pink to purple water clouds are yellow to white vegetated surfaces are green MODIS - False Color Phase Image

1.6 µm reflectance varies as a function of optical thickness more for water clouds than ice clouds 11 µm BT varies as a function of optical thickness more for ice clouds than for water clouds MAS data from single-layered cirrus and water phase clouds From Baum and Spinhirne (2000), Figure 2a RT simulation of a cirrostratus cloud RT simulation of a water cloud

MAS data from overlap region falls between single layer water and cirrus cloud data in R[1.63 µm] and BT[11 µm] space MAS data from cirrus overlying water phase cloud From Baum and Spinhirne (2000), Figure 2b RT simulation of a cirrostratus cloud RT simulation of a water cloud

Separate clear sky from cloudy pixels Use MODIS cloud mask Find single-layer water cloud and single-layer ice cloud pixels Use µm brightness temperature difference Separate overlapped cloud pixels from single layer cloud pixels Infer the 11 µm brightness temperature and 1.6 µm or 2.1 µm reflectance for overlapped clouds based on those from single layer clouds Imager Cloud Overlap Detection Summary MODIS

11 µm brightness temperature Pixels in pink are assumed to be clear MOD35 Cloud Mask BT[11 µm] (K)

Simulations of Ice and Water Phase Clouds µm BT Differences High Ice clouds BTD[8.5-11] > 0 over a large range of optical thicknesses τ T cld = 228 K Midlevel clouds: BTD[8.5-11] values are similar (i.e., negative) for both water and ice clouds T cld = 253 K Low-level, warm clouds: BTD[8.5-11] values always negative T cld = 273 K Ice: Cirrus model derived from FIRE-I in-situ data * Water: r e =10 µm Angles   = 45°,  = 20°, and  40° Profile: midlatitude summer

Single-layer Ice and Water Clouds Water BT[11 µm] (K) Ice

For an NxN block of pixels, where N usually is 200 Overlap Detection

Potentially overlapped pixels are in red

600 km MODIS block 11 Dec., 2002 with 1 pass cloud overlap product

Overlap Detection Tiling

600 km MODIS block 11 Dec., 2002 with 16 pass cloud overlap product

MODIS image with ER-2 flight track from 19:11 to 19:22 overlaid Color gradations every 1 minute 200 x 200 km

MODIS image with ER-2 flight track from 19:11 to 19:22 overlaid Color gradations every 1 minute 200 x 200 km

Cloud Physics Lidar (CPL) cloud boundaries

Cloud Physics Lidar (CPL) Backscatter and Depolarization

TX-2002: 10 Dec., 2002 ER-2 flight track overlaid on GOES-8 visible image Note: Problem with Nav. recorder on this day.

MODIS image with ER-2 flight track from 17:00 to 17:11 overlaid Color gradations every 1 minute 17:00 17:11

MODIS image with ER-2 flight track from 17:00 to 17:11 overlaid Color gradations every 1 minute 17:00

MODIS image with ER-2 flight track from 17:00 to 17:11 overlaid Color gradations every 1 minute 17:00 17:11 No overlap detected along flight track

MODIS image with ER- 2 flight track from 17:00 to 17:11 overlaid Color gradations every 1 minute No overlap detected along flight track

Filter out midlevel clouds when three clouds layers are present Remove thin cirrus contamination of clear sky over ocean Expand upon case studies with CPL validation during TX and CRYSTAL-FACE include lidar depolarization and and optical thickness information Apply algorithm to full day of MODIS data Overlap detection code in C Near real time direct broadcast application: imminent Investigation into multilayer effects on cloud property retrievals Quality and tendencies in cloud overlap conditions Combine with high-spectral resolution infrared data Retrieval of upper level cirrus cloud properties Future Plans

21 April, 2001 at 1745Z ARM Southern Great Plains Site Lidar shows low level clouds MMCR shows upper level clouds

Raman Lidar detects high cloud throughout the day MMCR sees only some of the high cloud. Low level return is difficult to identify Another Lidar/Radar Comparison