U.S. JGOFS Synthesis & Modeling
DATA: Guidelines for
Preparing Gridded Data Sets for the LAS
For gridded dataset we strongly recommend that
investigators supply their data in netCDF
format and adhere to the COARDS and
The following 3 questions will help identify any special
handling required for your data. If you answer YES to any
of these questions, please contact the U.S. JGOFS Data Management Office via request form.
1. Is the grid lon-lat-depth-time curvilinear?
(i.e. not rectilinear)
Posting curvilinear grids on the LAS system
requires special handling
2. Are there special visualization requirements?
(e.g., palette, masking, levels)
An example of this is where your data
requires displaying on some non-linear scale.
3. Does the dataset consist of multiple files that
need to be strung together?
1. Specify which variables from this dataset should be
(can be) displayed with LAS
2. Every variable must have the following three
attributes:units, missing_value and
3. Although LAS doesn't require it, the global
attributes should include: description,
authors and date.
4. If it's a global data set, LAS also expects the
longitude axis to have: LON:modulo = " "
If you are familiar with netCDF or Ferret,the following
additional checks might also prove useful:
ncdump -h ~file~
1. Do the dimensions appear again as variables?
2. Are the axis units defined? Are they ones that
3. Do the data variables have reasonable titles and
4. Is the missing value flag specified?
start FERRET and look at the
|1. USE ~file~
- can ferret read the data?
|2. SHOW DATA
- are the variables and their units
|3. SHOW GRID
- are the grid dimensions sensible?
- are the modulo axes understood?
|4. SHADE ~var~
- does the plot look reasonable?
- does it need a land mask?
- is it right side up?
- are the missing values understood?
METADATA EXAMLE: An example of what LAS considers
adequate metadata is shown below. This is the 'ncdump -h
filename' listing for the Global SeaWiFS Chlorophyll data
currently listed on the SMP LAS, in the Ocean Color category.
ncdump -h SeaWiFS_data.nc
LONGITUDE = 360 ;
LATITUDE = 180 ;
TIME = 138 ;
float LONGITUDE(LONGITUDE) ;
LONGITUDE:units = "degrees_east" ;
LONGITUDE:long_name = "Longitude" ;
LONGITUDE:point_spacing = "even" ;
float LATITUDE(LATITUDE) ;
LATITUDE:units = "degrees_north" ;
LATITUDE:long_name = "Latitude" ;
LATITUDE:point_spacing = "even" ;
double TIME(TIME) ;
TIME:units = "days since 1950-01-01 00:00:00" ;
TIME:long_name = "Time" ;
TIME:time_origin = "1-JAN-1950" ;
TIME:point_spacing = "uneven" ;
float CHLOROPHYLL(TIME, LATITUDE, LONGITUDE) ;
CHLOROPHYLL:units = "mg/m^3" ;
CHLOROPHYLL:long_name = "Chlorophyll" ;
CHLOROPHYLL:missing_value = "1e+35" ;
:Title = "Global SeaWiFS chlorophyll 8 day composites"
:authors = "J. Yoder & M. Kennelly" ;
:date = "26 July, 2001" ;
These guidelines were kindly drafted by Jon Callahan
of NOAA/PMEL, and Cyndy Chandler of WHOI
Draft: 29 Jan 2001
Updated: 17 Sep 2001