ReadMe file for MODIS-derived global snow/cloudiness map products (SNWFG, CLDFR)

This product contains half-monthly averaged global snow cover extent and cloudiness distribution derived from MODIS 5km resampled radiance data (MOD02SSH, MYD02SSH).
The product file is generated every half-month (1st-15th, 16th-the last day of each month). On the last day of each month, a monthly product, which is an aggregated product of two half-monthly products, is generated.

Latest version is ver.304 (released on 30 June, 2014).
When comparing with old versions, please note on the following revision history.

Note also that the product files are possilbly updated at any time due to version up of the analysis software.

-Revision history
-Definition of the output file

-Naming rule of binary file

E.g., MDS20081116_20081130_GLBOD0HM_PPPPP_EQ05KM_301.dat
MDS:MODIS
20081116:YYYYMMDD, the first date of snow cover observation
20081130:YYYYMMDD, the last date of snow cover observation
GLBOD0:GLoBal, Observation of Daytime
HM:Half-Monthly ("1M" for Monthly product)
PPPPP:Product ID ("SNWFG" for snow cover, "CLDFR" for cloudiness)
EQ05KM:global EQuirectangular (lat-lon) projected 5KM resolution grid (JASMES Global grid: 7200×3601)
301:Product version
.dat:Extention (dat: binary data, hdf: HDF4 formatted data)

-Format of binary file
 Size of header: number of pixel(7200) × 1byte
  Stored information: the number of pixel, the number of line, minimum longitude, maximum latitude, grid interval
  Format: 2I6, 2f8.2, f8.4
 Data size: 7200 pixel × 3601 line (data type: uint8)
 Size of pixel (same as grid interval): 0.05 degree
 Latitude and longitude of four corners of the global image (center of each corner pixel):
  Upper left: Lon: 0.0deg.E, Lat: 90.0deg.N
  Lower right: Lon: 359.95deg.E (-0.05deg.W), Lat: 90.0deg.S
- Definition of Snow Cover Flag
- Meaning of "Surface_Flag" (SD name) stored in SNWFG file
[Half-monthly product]
 [Ocean Flags]
00:cloud over water
05:open water
07:polar night over water
01:dry snow & ice over water (high conf.)
03:dry snow & ice over water (low conf.)
201:wet snow & ice over water (high conf.)
203:wet snow & ice over water (low conf.)
09:no data over water
 [Land Flags]
10:cloud over land
15:land (non-snow cover)
17:polar night over land
11:dry snow over land (high conf.)
13:dry snow over land (low conf.)
211:wet snow over land (high conf.)
213:wet snow over land (low conf.)
19: no data over land
Note: Possibility of the existence of snow cover is evaluated and classified into three confidence levels (high conf., low conf., and (non-snow) land or open water) based on the frequency of clear (non-cloudy) sky and snow cover dates during the half-month period.
Snow(high conf.):if Num of Clear day >= 3 & Num of Snow day >= 1
& Ave of BT11um, clear <= 10 deg.C
Snow(low conf.):else if Num of Clear day < 3 & Num of Snow day >= 1
& Ave of BT11um, clear <= 10 deg.C
Land/Open water::else
In addition, dry and wet snow covers are discriminated based on threshold tests using reflectance at near-infrared band and brightness temperature at 11 micron.
[Monthly product]
 [Ocean Flags]
00: cloud over water
05:open water
07: polar night over water
01: dry snow & ice over water (very high conf.)
02: dry snow & ice over water (high conf.)
03: dry snow & ice over water (middle conf.)
04: dry snow & ice over water (low conf.)
101: dry/wet mixed snow & ice over water (very high conf.)
102: dry/wet mixed snow & ice over water (high conf.)
103: dry/wet mixed snow & ice over water (middle conf.)
104: dry/wet mixed snow & ice over water (low conf.)
201: wet snow & ice over water (very high conf.)
202: wet snow & ice over water (high conf.)
203: wet snow & ice over water (middle low conf.)
204: wet snow & ice over water (low conf.)
09: no data over water
 [Land Flags]
10:cloud over land
15:land (non-snow cover)
11:dry snow over land (very high conf.)
12:dry snow over land (high conf.)
13:dry snow over land (middle conf.)
14:dry snow over land (low conf.)
17ížpolar night over land
111:dry/wet mixed snow over land (very high conf.)
112:dry/wet mixed snow over land (high conf.)
113:dry/wet mixed snow over land (middle conf.)
114:dry/wet mixed snow over land (low conf.)
211:wet snow over land (very high conf.)
212:wet snow over land (high conf.)
213:wet snow over land (middle conf.)
214:wet snow over land (low conf.)
Note: Possibility of the existence of snow cover for monthly product is evaluated and classified into five confidence levels (very high conf., high conf., middle conf., low conf., and (non-snow) land or open water) based on the following equation using the two Surface_Flag data from the former and latter half-monthly products.
Ocean: Monthly flag = (former half-month flag + latter half-month flag)/2
Land: Monthly flag = (former half-month flag + latter half-month flag - 20)/2 +10
E.g., when the former half-month flag is 11 and the latter is 213, monthly flag will be (11 + 213)/2 = 112 and the pixel is identified as dry/wet mixed snow over land (high conf.).
In this context, as shown above when dry and wet snow conditions are mixed in a month, monthly flag is identified as "dry/wet mixed snow cover".
Otherwise, snow cover is identified as either dry or wet snow in the monthly products.

Another important assumption in this snow cover product is that the land pixels under the polar night are assumed to be covered with dry snow cover when counting snow cover extents (global, northern hemisphere, southern hemisphere etc.).
•Meaning of stored values in "Snow_Dates" and "Clear_Dates"
These SD data are stored only in the HDF formatted file (***.hdf). Snow_Dates is a record of snow detection dates during the corresponding month expressed in the 32-bit field [32-bit unsigned integer].
Clear_Dates is also the same except for that the dates of clear sky are recorded. Bit-0 (right edge) indicates ocean (0) or land(1), and bit-1-31 expresses the date of snow or clear day. For example, "100101001" (bit 9-31 are all zero) indicates that the pixel is land and the pixel area was covered with snow (or under clear sky) on 3rd, 5th and 8th of the corresponding month.

- Definition of Cloudiness Products

- Format of ASCII output file (MDS_SNW_GLB.txt)
YYYY MM D1 D2 WWWWWWWWWW NNNNNNNNNN SSSSSSSSSS sssss001 sssss002 ..... sssss137
  AAAAAAAAAAAW AAAAAAAAAAAN AAAAAAAAAAAS VVVVVVVVVVW VVVVVVVVVVN VVVVVVVVVVS vvvvv001 vvvvv002 ..... vvvvv137
   ..... TTTTTTTTTTTT TTTTTTTTTTTN TTTTTTTTTTTS ttttttttt001 ttttttttt002 ..... ttttttttt137
where
YYYY:year
MM:month
D1:first day of observation
D2:end day of observation
WWWWWWWWWWWW:Area of land snow cover extent on the whole globe in km2
NNNNNNNNNNNN:Area of land snow cover extent in the northern hemisphere in km2
SSSSSSSSSSSS:Area of land snow cover extent in the southern hemisphere in km2
sssssssss***:Area of land snow cover extent in individual countries in km2
AAAAAAAAAAAW:Area of land on the whole globe in km2
AAAAAAAAAAAN:Area of land in the northern hemisphere in km2
AAAAAAAAAAAS:Area of land in the southern hemisphere in km2
VVVVVVVVVVVW:Area of clear region on the whole globe (area of valid pixels) in km2
VVVVVVVVVVVN:Area of clear region in the northern hemisphere (area of valid pixels) in km2
VVVVVVVVVVVS:Area of clear region in the southern hemisphere (area of valid pixels) in km2
vvvvvvvvv***:Area of clear region in individual countries in km2
TTTTTTTTTTTT:Area of land wet snow cover extent on the whole globe (area of valid pixels) in km2
TTTTTTTTTTTN:Area of land wet snow cover extent in the northern hemisphere (area of valid pixels) in km2
TTTTTTTTTTTS:Area of land wet snow cover extent in the southern hemisphere (area of valid pixels) in km2
ttttttttt***:Area of land wet snow cover extent in individual countries in km2
** denotes asigned number of country (e.g., 1: Korea, 2: China ...).
Note: Definition of ID number of each country or region is shown at the bottom of this document.

- Format of ASCII output file (MDS_CFR_GLB.txt)
YYYY MM D1 D2 WWWWWWWW NNNNNNNN SSSSSSSS ccccc001 ccccc002 ..... ccccc137 cccczm01 ...cccczm18
where
YYYY:year
MM:month
D1:first day of observation
D2:end day of observation
WWWWWWWW:Half-monthly mean of cloud fraction over land on the whole globe in %
NNNNNNNN:Half-monthly mean of cloud fraction over land in the northern hemisphere in %
SSSSSSSS:Half-monthly mean of cloud fraction over land in the southern hemisphere in %
ccccc***:Half-monthly mean of cloud fraction in individual countries in %
cccczm@@:Half-monthly mean of cloud fraction in individual latitudinal zone in %
** denotes asigned number of country (e.g., 1: Korea, 2: China ...).
@@ denotes asigned number of latitudinal zone (e.g., 1: 90-80N, 2: 80-70N, ... 17: 80-90S).
Note: Definition of ID number of each country or region is shown at the bottom of this document.

- Definition of country or region
ID number is assigned to individual country and/or region at which snow covered area or cloudiness are estimated and stored in the ASCII output files. The followings are the definition of ID numbers used in this product.
Asia
1-6East Asia
1Korea
2China
3North Korea
4Japan
5Mongolia
6Taiwan
7-15Southeast Asia
7Indonesia
8Cambodia
9Thailand
10Philippines
11Brunei Darussalam
12Vietnam
13Malaysia and Singapore
14Myanmar
15Laos
16-22South Asia
16India
17Sri Lanka
18Nepal
19Pakistan
20Bangladesh
21Bhutan
22Others
23-27Central Asia
23Uzbekistan
24Kazakhstan
25Kyrgyz
26Tajikistan
27Turkmenistan
28-31West Asia (incl. Middle East, Turkey)
28Afganistan
29Iran
30Turkey
31Others (Arabian Peninsula)
Africa
32-36North Africa Aria
32Algeria
33Egypt
34Tunisia
35Morocco (incl. Western Sahara)
36Libya
37-41Sahara Desert Area
37Sudan
38Chad
39Niger
40Mali
41Mauritania
42-47Area around the Gulf of Guinea
42Ghana
43Cote d'Ivoire
44Senegal
45Nigeria
46Burkina Faso
47Others (Guinea, Liberia and other 9 nations)
48-53Tropical Rainforest Area
48Gabonese
49Cameroon
50Republic of Congo
51Democratic Republic of the Congo
52Republic of Equatorial Guinea
53Central African Republic
54-61South Africa Aria
54Angola
55Zambia
56Zimbabwe
57Namibia
58Botswana
59South Africa
60Mozambique
61Others (Malawi, Lesotho, Swaziland)
62-66East Africa Area
62Ethiopia, Eritrea
63Kenya
64Somali
65Tanzania
66Others (Uganda, Djibouti, Rwanda, Burundi)
67-68Indian Ocean Aria
67Madagascar
68Others (Comoros, Seychelles, Mauritius, Reunion)
Europe
69-92EU
69Ireland
70United Kingdom
71Italy
72Estonia
73Austria
74Hellenic Republic (Greece)
75Sweden
76Spain
77Slovakia
78Slovenia
79Czech Republic
80Denmark
81Germany
82Hungary
83Finland
84France
85Bulgaria
86Poland
87Portugal
88Latvia
89Lithuania
90Romania
91Netherlands, Belgium, Luxembourg
92Others
93-107non-EU
93Iceland
94Azerbaijan
95Albania
96Armenia
97Ukraine
98Georgia
99Croatia
100Swiss
101Serbia, Montenegro
102Norway
103Belarus
104Bosnia and Herzegovina
105Macedonia
106Moldova
107Others
Russia
108West Russia (west of 60 deg. East)
109West Siberia (60-90 deg. East)
110Central Siberia (90-120 deg. East)
111East Siberia (120-150 deg. East)
112Far Eastern Region (East of 150 deg. East line)
North America (North of Panama)
113USA (incl. Hawaii, excl. Alaska)
114Alaska
115Canada
116Mexico
117Others
South America
118Argentine
119Uruguay
120Ecuador
121Guyana
122Colombia
123Suriname
124Chile
125Paraguay
126Brazil
127Venezuela
128Peru
129Bolivia
130French Guiana
131Others
Oceania
132Australia
133New Zealand
134Others
Polar Regions etc.
135Greenland
136Antarctica
137Svalbard and Jan Mayen

EORC/JAXA
2014.06.30