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

• 30 June 2014 (Ver.301 -> 304): revised points
  - Overestimations of wet snow cover seen in autumn season are reduced.
  - File name of binary data is inserted into the last column of the output file (MDS_SNW_GLB.txt, MDS_CFR_GLB.txt)
  - Flag value of no data pixel in half-monthly products was changed from 0 or 10 (same as cloudy pixel) to 255.
  
• 27 December 2011 (Ver.100 -> 301, applied from Oct. 2011): revised points
  - Ability to detect snow cover over cold desert area in China and central Asia were improved.
  - Flags for snow cover over sea ice were added.
  - Dates of snow detection and clear sky for each pixel are newly included in the output (HDF file only).
  
• 10 March 2010 (Ver.100)
  - Description on the format of the output file (MDS_SNW_GLB.txt) was corrected.
  
• 08 November 2009 (First release Ver.100)

-Definition of the output file

• - Binary file of snow cover flag generated every half-month (.dat, .hdf)
• - Binary file of snow cover flag generated every month (.dat, .hdf)
• - ASCII file containing the number of snow over land pixel, valid data pixel, snow covered area of each country etc. (MDS_SNW_GLB.txt)
• - ASCII file containing the averaged cloudiness (rate of cloudy day in %) over land estimated for global, northern and southern hemisphere, and each country etc. (MDS_CFR_GLB.txt)

-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.)
17	：	polar 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

• - Meaning of stored values in CLDFR file
  

  0-200	:	cloudiness (0-100%)
  255	:	no data (e.g., due to polar nights)

• - Definition of cloudiness
   Rate of cloudy dates during half-month (when there are four days of cloudy during a half-month period of 15 days, cloudiness is identified as 26.7%. Monthly value is an average of two half-monthly values.

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

EORC/JAXA
2014.06.30