Measurements at a sea platform have shown that the Ocean Surface Albedo (OSA) is very dynamic and highly variable (see examples). Based on our years of observation data and the validated Coupled Ocean-Atmosphere Radiative Transfer (COART) model (for validation examples, see figures in Jin et al., 2005 ), an OSA Look Up Table (LUT) was created in terms of four most sensitive and readily available parameters: the solar zenith angle (SZA), wind speed, aerosol/cloud optical depth, and ocean chlorophyll concentration (Chl). With the LUT and attached reading code, the user can easily obtain the OSA in any spectral band for any combination of the four parameters ( try it online.) This albedo scheme was originally developed for the atmospheric radiation budget retrieval for NASA's CERES project (PI: Bruce Wielicki). But it can be easily applied to a radiative transfer or climate model.
The LUT below has 16x15x7x5=8400 records, which represent
* 16 aerosol/cloud optical depth (Tau < 1.0 as aerosol, Tau >1.0 as cloud):
0.0, 0.05, 0.1, 0.16, 0.24, 0.35, 0.5, 0.7, 0.99, 1.3, 1.8,
2.5, 5.0, 9.0, 15.0, 25.0;
* 15 solar cosine zeniths:
0.05, 0.09, 0.15, 0.21, 0.27, 0.33, 0.39,
0.45, 0.52, 0.60, 0.68, 0.76, 0.84, 0.92, 1.00;
* 7 wind speeds (m/s): 0, 3, 6, 9, 12, 15, 18;
* 5 ocean chlorophyll concentrations (mg/m3):
0.0, 0.1, 0.5, 2.0, 12.0
Three tables with different spectral resolutions are provided here. Basically, you only need the high resolution 24 band table. The other two (broadband and 4 band tables) can be produced by the 24 band table. However, the 4 bands and broadband are widely used, so two additional tables are created for convenience, which are much smaller in size.
Albedo table (24 bands) (binary)
Reading code readalb.f
Albedo table (4 bands: 0.20-0.69; 0.69-1.19; 1.19-2.38; 2.38-4.0um) (binary)
Reading code readalb4.f
Broadband albedo table (0.20-4.0um) (binary)
Reading code readalb1.f
(Note: If your system use WORDS instead of BINARY as record length unit, you must
change the "recl" parameter in the OPEN statements in the reading code (i.e., divide it
by 4). Otherwise, you may read the wrong record or get error message on invalid
record number. Also, the binary is in
Big Endian format.
If your sestem (like PC) uses "Little Endian", you need to
convert the table format.
To be sure, you should compare few cases with the
online calculations.)
If you still have problem with the binary files, here is the tables in ASCII format:
ocnalbtab24bnd.txt (24 bands);
ocnalbtab4bnd.txt (4 bands);
ocnalbtab1bnd.txt (1 band)
This LUT albedo is implemented in the Langley version of Fu-Liou code, in which a Modular Subroutine in F90 does a onetime read of the entire table and outputs albedo in the 15 Fu-Liou bands. You may do similar modification for your application.
Except for the four parameters selected here, many other parameters, such as
ozone, water vapor, and cloud height, also affect the OSA, but those influences
are much smaller under most conditions.
This figure
shows the cloud height effect, which is small unless the cloud is very thin.
Ocean sediments may also be important for OSA,
but significant sediment loadings are confined to some coastal regions.
Ocean Chl effect is mainly in the visible spectrum and hence the OSA spectral shape.
It decreases albedo in the blue but increases albedo in the green; the combined
effect on the broadband albedo is small. In addition, the Chl in majority of the
global ocean is low (
see Chl climatologies). Therefore, neglecting the Chl variation by simply using a
constant (e.g., a global average about 0.15 mg/m3) might be sufficient for some
applications such as atmospheric GCM. The LUT do not include the effect of foam,
which may be significant at high wind speeds (larger than 15 m/s). Users may
choose to add one of those empirical corrections to our LUT for OSA.
This figure displays
color contours of ocean albedo versus the SZA and wind speed.
For questions or comments, please contact:
Zhonghai Jin or Thomas Charlock.
For more information, read the following reference.
Reference:
Jin, Z., T. Charlock, W. Smith Jr., and K. Rutledge, 2004:
A parameterization of ocean surface albedo. Geophys. Res. Let., 31, L22301,
doi:10.1029/2004GL021180.
Jin, Z., T.P. Charlock, K. Rutledge, K. Stamnes, and Y. Wang,
Analytical
solution of radiative transfer in the coupled atmosphere-ocean system
with a rough surface. Appl. Opt., 45, 7443-7455 (2006).
Notice:
Tables in ASCII format are available.
Go to CO-ART modeling online
Try the albedo LUT online