aerosols observations from modis
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Aerosols Observations from MODIS. Pawan Gupta NASA ARSET- AQ – California Training September 10-12, 2013. ARSET - AQ A pplied R emote S ensing E ducation and T raining – A ir Q uality A project of NASA Applied Sciences. Topic covered…. EOS satellites MODIS on Terra and Aqua - PowerPoint PPT PresentationTRANSCRIPT
Aerosols Observations from MODIS
Pawan GuptaNASA ARSET- AQ – California Training
September 10-12, 2013
ARSET - AQApplied Remote Sensing Education and Training – Air Quality
A project of NASA Applied Sciences
Topic covered…
• EOS satellites• MODIS on Terra and Aqua• Data Products • Atmospheric Data Products• Aerosols Data …
Five Instruments:• ASTER• CERES• MISR• MODIS• MOPITT
Terra Spacecraft
Aqua Spacecraft
Six Instruments:• MODIS• CERES• AIRS• AMSU - A• AMSR - E • HSB
Satellite Remote Sensing Instrument - MODIS
Newer Earth-observing satellite remote sensing instruments typically make observations at many discrete wavelengths or wavelength bands.
36 wavelength bands covering the wavelength range
405 nm (blue) to 14.385 μm (infrared)
MODIS – MODerate resolution Imaging Spectroradiometer
MODIS products are divided into three main categories
Due to the size and variety of products there is no single sourcefor information about the MODIS products.
Atmosphere
Land
Ocean
Level 1 Products - Raw data with and without applied calibration.
Level 2 Products - Geophysical Products (sometimes gridded)
Level 3 Products - Globally gridded geophysical products
This structure is common to many satellite products
Data Levels
Level 1 Products – Raw or calibrated radiances
Level 2 Products – Geophysical products
Less Processing
More Processing
Granules
Level 3 Products – Global composites
Global compositesof level 2 granules
MODIS Product Hierarchy
Granule - A 5 minute piece of an orbitUsed to produce
Granules
Used to produce
Understanding a MODIS File Name
MOD04_L2.A2001079.0255.005.2006289012028.hdf
Product Name Date - year, Julian day
Time Collection
File processing information
Aerosol Product Filename
MOD - Terra product MYD - Aqua product
Few more things to know about MODIS DATA
• All MODIS products come in HDF format • In HDF format each file contains both data and
metadata
• SDS - Each parameter within a MODIS HDF file is referred to as an SDS (Scientific Data Set)
• An SDS must be referenced precisely according to name when analyzing the data with your own computer code.
• Calibration accuracy.
• Quality Assurance – product creators estimate• of the quality of the data.
• Data formats.
• Product Resolutions.
• How level 3 products are created from level 2• temporally and spatially.
• Current release of the data and data history.
And therefore you need to learn!
Things that change with each instrument
Fundamental Inputs• Separate Algorithms for Ocean and Land• Calibrated and Geolocated Reflectances (MOD02, MOD03, Errors <2%)• Surface Information (land, water, desert)• Meteorological Data from NCEP• Other Ancillary data sets
MODIS Aerosol Products
Land Ocean
Dark Target Deep Blue – Used over bright land surfaces
Three Separate Algorithms
Currently the dark target and deep blue products are separate.When both are available the user must select which one to use
In collection 6 there will be a joint product that uses an automatedprocedure to select the appropriate product.
MODIS Aerosol ProductsAll three algorithms create a 10 Km product.Land and Ocean 400 half kilometer pixels. Deep Blue 100 one kilometer pixelsOcean and Land (dark target) algorithms assume that aerosols brighten the scene.
Retrievals can only occur where there are asufficient number of spectrally dark pixels.
MODIS Aerosol Products
Important Points to Remember for MODIS Aerosol Products- Ocean and Land Products are produced using totally separateand distinct algorithms. All current Level 2 aerosol products are at 10 Km (10 x 10) resolution.
- The most important products for air quality are Aerosol Optical Depth. These exist for both Ocean and Land. - The most current version of Aerosol Product is collection 5 and collection 6 should release soon.
MODIS Aerosol SDS
The individual Land or Ocean SDS is generally preferred because - it contains more wavelengths - gives more information about quality - at level 3 it gives a quality weighted product that screens out anomalies
Land_And_Ocean Is useful if you need both together but may not give the same results as Land or Ocean
The Ocean and Land algorithms each produce their own Scientific Data Sets or SDS’s. When both algorithms retrieve the same parameter they may be combined into a joint Land_and_Ocean SDS.
MOD04 Aerosol Products MYD04Main Products - Ocean
Effective_Optical_Depth_Average_OceanRetrieved AOD at .47, .55, .66, .86, 1.24, 1.63, 2.13
Optical_Depth_Ratio_Small_Ocean_0.55*Fraction of Fine Mode AOD at 0.55
Optical_Depth_Small_Average_OceanAOD * Fine Mode Ratio
AOD
FineFraction
FineAOD
Main Products - Land
Corrected_Optical_Depth_LandRetrieved AOD at .47, .55, and .66
Optical_Depth_Ratio_Small_LandFraction of Fine Mode AerosolNot reported for AOD < 0.2
Optical_Depth_Small_LandAOD * Fine Mode Ratio(may be a threshold)
A Qualitative Product Only!
Aerosol Products
Main Products - Land
Corrected_Optical_Depth_LandRetrieved AOD at .47, .55, and .66
Optical_Depth_Ratio_Small_LandFraction of Fine Mode AerosolNot reported for AOD < 0.2
Optical_Depth_Small_LandAOD * Fine Mode Ratio(may be a threshold)
Aerosol Products
AOD
FineFraction
FineAOD
Quality Assurance is Extremely Important!!
Quality_Assurance_OceanScale is 0 - 3
Recommend Ocean QA above 0
Factors:Number of pixelsError fittingHow close to glint
QA indicates the confidence in the quality of the retrieval.
Quality_Assurance_LandScale is 0 - 3
Recommend Land QA of 3
Factors:Number of pixelsError fittingSurface reflectance
Optical_Depth_Land_and_OceanImage_Optical_Depth_Land_and_Ocean
For Visualization purposes when youwant an image of as much of the sceneas possible.This SDS includes poor quality(QA level 0) data
Corrected_Optical_Depth_Land
Daily L3 aerosol optical thickness over land and ocean
The large gaps over ocean are due to Sunglint The gaps over land are due to bright surfaces and and clouds Regularly spaced gaps near the equator are due to lack of coverage between orbits.
Fires: Zambia, day 205, 2005. 1 km resolution of AOT allows tracing smoke plumes
-0.50-0.250.000.250.500.751.001.251.50
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
0.0 0.2 0.4 0.6 0.8
MAIAC
MOD04
Aerosol Retrievals: Biomass Burning
Land Algorithm…• First Step: Organize reflectance in three channels (0.47, 0.67, and 2.13) into 10X10 Km box (20X20 =400 Pixels) at 500 m resolution
20 Pixels (10 Km)
20 P
ixel
s (1
0 K
m)
Remer et al., 2005
Dark Target Algorithm Summary(Land)
1) Screen out unwanted features
- clouds - water - snow/ice pixels
Land Algorithm…Pixel Selection• The 400 pixels in the box are evaluated pixel by pixel to identify whether the
pixel is cloudy, snow/ice, or water
• The land algorithm will retrieve aerosol for coastal boxes that contain one or more pixels identified as ocean, but will decrease the quality of that land retrieval
• An ocean retrieval requires all 400 pixels in the box to be identified as water
• Cloud mask based on spatial variability to identify low clouds • The reflectance in the 1.38-m channel to identify high clouds
• The algorithm is sensitive to small subpixel patches of snow/ice, now all eight pixels contiguous to a pixel identified as “snow/ice” by MOD35 will also be labeled as “snow/ice.”
• The pixels are further screened for subpixel water by determining NDVI for each pixel. NDVI values less than 0.10 are identified as containing subpixel water and are excluded along with cloudy and snowy pixels from the remainder of the algorithm
Remer et al., 2005