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5.0 Satellite Imagery - Basic Concepts

McIDAS can process images from geostationary and polar orbiting satellites. Geostationary satellites remain above a fixed location on the earth's surface, appoximately 22,236 mi above the equator. Because the satellites rotate with the earth, they always observe the same portion of the globe.

Currently, GOES-East observes North and South America and the western Atlantic Ocean. GOES-West monitors North America and the north and south portions of the eastern Pacific Ocean. EUMETSAT has two satellites (METEOSAT/MSG) which monitor Europe, Africa, western Asia and the eastern Atlantic Ocean. JMA has a satellite (GOES-Pacific/MTSAT) which monitors eastern Asia, Australia, the western Pacific Ocean and the eastern Indian Ocean. GOES-Pacific is a United States satellite that has been loaned to JMA after the failure of GMS. GOES-Pacific will monitor the areas GMS covered until MTSAT is launched.

The image below shows the coverage of each geostationary satellite:

Polar orbiting satellites orbit at much lower altitudes (800-900 km). Their path is 2,400 km wide centered at the orbit path. With each orbit, the satellites observe a new path. Currently, SSEC ingests a variety of POES satellites including: NOAA-12, NOAA-14, NOAA-15, NOAA-16, NOAA-17, Aqua, and Terra.

Satellite Data Storage

In McIDAS, satellite data is stored in locations on disk called areas. You can copy, change, display, and delete areas. Areas contain both data and area directories. Area data can be displayed in McIDAS image frames. The area directory contains descriptive information, such as the sensor source, image date, picture start time, and image coordinates. To see this information, use the IMGLIST command, as shown below:

Image file directory listing for:GV4 
 Pos Satellite/         Date       Time      Center      Res (km)   Image_Size       
     sensor                                 Lat  Lon    Lat   Lon    
 --- -------------  ------------  --------  ---- ----  ----- ----- ------------
   1 GOES-7        13 MAR 93072  17:01:00    26   87                         
    Band: 1   0.65 um Daytime cloud detection            4.0   4.0  1335 x 1608
     proj:    0 created: 1993208 191703  memo: AAA-MSI TO VIS      VIA ARCHIVE
     type:VISR     cal type:BRIT                                             
     offsets:  data=  768 navigation=  256 calibration=    0 auxillary=    0
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   4       
     valcod: 1104210435 zcor:  1 avg-smp: A                               
     start yyddd: 1993072  start time:170105  start scan:   56           
     lcor: 1121  ecor:  7585  bytes per pixel: 1  ss: 32                
     Image Center Point Res (derived)  Lat:   4.37 (km)  Lon:   3.64 (km) 
IMGLIST: done     

Area Naming Conventions

Areas conventionally use the naming convention AREAnnnn where nnnn is the four digit area number. For example, AREA0003 is the name of the file that contains area 3. Most of the older McIDAS commands use only the area number. However, you must use the AREA prefix with the DMAP command or when using Unix commands to copy, move, or delete areas.

In ADDE, sequences of AREA files are grouped together in a dataset. For example, in a previous lesson, you created the dataset MYDATA/IMAGES, which contains the AREA file numbers from 1 to 9999. Individual AREA files can be accessed with their position number within the dataset. In the case of MYDATA/IMAGES, position 3 (MYDATA/IMAGES.3) would relate to the file AREA0003. However, in the dataset MYDATA/TEST-IMAGES that was created in the previous lesson, the dataset defined the AREA files ranging from 4000 to 4004, so position 3 (MYDATA/TEST-IMAGES.3) would be AREA4002. (This would be equivalent to MYDATA/IMAGES.4002)

Image Sectors

Complete images are often too large to display on a frame. You can subsect the original area into another area or onto a frame with increased, decreased, or the original resolution. This is useful when copying areas. These subsections of the original area are called image sectors. An image sector can be created four ways:

The sampling and/or averaging rates are listed as the Res in the IMGLIST output (Lat=ER, Lon=LR). These additional descriptors enable the system to compute the image coordinate of the Jth element in the Ith line in an image sector by means of the following calculations:

LINE = LCOR + (I-1) * LR

The number of lines and elements extracted from the original image (LSIZ, ESIZ) determines the size of the image sector.

Unidata's Real-time Image Data

Unidata sites receiving the Unidata-Wisconsin data stream have access to imagery from GOES-East and GOES-West as well as some additional products (ex: Antarctic composite, Manually Digitized Radar image).

Unidata-Wisconsin Datastream Imagery
Imagery Data type AREA numbers ADDE dataset names
GOES-East/West H2O Composite 70-79RTIMAGES/GEW-WV
GOES-East/West IR Composite 80-89RTIMAGES/GEW-IR
GOES-East/West VIS Composite 90-99RTIMAGES/GEW-VIS
Mollweide Composite IR 100-109RTIMAGES/MOLL-IR
Mollweide Composite H2O 110-119RTIMAGES/MOLL-WV
GOES-West Western US IR 130-139RTIMAGES/GW-IR
GOES-East North America VIS 140-149RTIMAGES/GE-VIS
GOES-East North America IR 150-159RTIMAGES/GE-IR
GOES-West Western US H2O 170-179RTIMAGES/GW-WV
Antarctic IR Composite 190-199RTIMAGES/ANTARCTIC
Manually Digitized Radar 200-209RTIMAGES/MDR
GOES-East North America H2O 210-219RTIMAGES/GE-WV
Mollweide IR/TOPO Composite 270-279RTIMAGES/MOLL-IRTOPO
GOES-East North America 3.9 um IR 1220-1229RTIMAGES/GE-39
GOES-East North America 13.0 um IR 1230-1239RTIMAGES/GE-CO2
GOES-West North America 3.9 um IR 1230-1239RTIMAGES/GW-39
GOES-West North America 12.0 um IR 1240-1249RTIMAGES/GW-12
CIMSS Cloud Top Pressure product 1100-1109CIMSS/CTP
CIMSS Precipitable Water product 1110-1119CIMSS/PW
CIMSS Sea Sfc. Temperature product 1120-1129CIMSS/SST
CIMSS Lifted Index product 1130-1139CIMSS/LI
CIMSS CAPE product 1140-1149CIMSS/CAPE
CIMSS Ozone product 1150-1159CIMSS/OZONE
CIMSS Nth. Am. Wildfire ABBA product 1190-1199CIMSS/FIRESNH
CIMSS Sth. Am. Wildfire ABBA product 1200-1209CIMSS/FIRESSH

Unidata has reserved AREA numbers 1-1999 and 9000-9999 for products in this and other IDD data streams. If you are going to change the default AREA numbers for products, you need to avoid these AREA number ranges. The table below lists the default AREA numbers that are used for topography images contained in the Unidata McIDAS distribution.

Topography Imagery Distributed with Unidata McIDAS
Imagery Data type AREA number ADDE dataset names
Global Mercator9000TOPO/GLOB
North America - Mercator9010TOPO/MERC
Western Hemisphere9012TOPO/WHEMI
Southern Hemisphere9013TOPO/SPOLE
Northern Hemisphere9014TOPO/NPOLE
Global Mollweide9015TOPO/MOLL
GOES-East Center at 75W9016TOPO/GOESE
GOES-West Center at 135W9017TOPO/GOESW
US Radar projection9018TOPO/MDR
NW Quadrasphere9019TOPO/QUAD

Unidata sites can also subscribe to NNEXRAD or FNEXRAD IDD feeds to receive the full or floater sets, respectively, of NEXRAD Level III image products that are available in NOAAPORT. These products come in a zlib-compressed format that bears no relation to McIDAS AREA, but can still be served by McIDAS ADDE.

Imagery Data type ADDE dataset names
NEXRAD Base Reflectivity Tilt 1 RTNEXRAD/N0R
NEXRAD Base Reflectivity Tilt 2 RTNEXRAD/N1R
NEXRAD Base Reflectivity Tilt 3 RTNEXRAD/N2R
NEXRAD Base Reflectivity Tilt 4 RTNEXRAD/N3R
NEXRAD Composite Reflectivity RTNEXRAD/NCR
NEXRAD Layer Reflect SFC-24 K ft RTNEXRAD/N0L
NEXRAD Layer Reflect 24-33 K ft RTNEXRAD/N1L
NEXRAD Layer Reflect 33-60 K ft RTNEXRAD/N2L
NEXRAD 1-hour Surface Rain Total RTNEXRAD/N1P
NEXRAD 3-hour Surface Rain Total RTNEXRAD/N3P
NEXRAD Storm Total Rainfall RTNEXRAD/NTP
NEXRAD Radial Velocity Tilt 1 RTNEXRAD/N0V
NEXRAD Radial Velocity Tilt 2 RTNEXRAD/N1V
NEXRAD Radial Velocity Tilt 3 RTNEXRAD/N2V
NEXRAD Radial Velocity Tilt 4 RTNEXRAD/N3V
NEXRAD 248 nm Base Reflectivity RTNEXRAD/N0Z
NEXRAD Storm-Rel Mean Vel Tilt 1 RTNEXRAD/N0S
NEXRAD Storm-Rel Mean Vel Tilt 2 RTNEXRAD/N1S
NEXRAD Storm-Rel Mean Vel Tilt 3 RTNEXRAD/N2S

Unidata sites can to the FNEXRAD IDD feed to receive the NEXRAD Level III product composites created by the UPC.

Imagery Data type ADDE dataset names
NEXRAD 1 km Base Reflectivity Tilt 1 NEXRCOMP/1KN0R-NAT
NEXRAD 1 km Base Reflectivity Tilt 1 Floater NEXRCOMP/1KN0R-FLT
NEXRAD 2 km 1-hour Surface Rain Total NEXRCOMP/2KN1P-NAT
NEXRAD 4 km Storm Total Rainfall NEXRCOMP/4KNTP-NAT
NEXRAD 6 km Base Reflectiveity Tilt 1 NEXRCOMP/6KN0R-NAT
NEXRAD 10 km Radar Coded Message NEXRCOMP/10KRCM-NAT

Users with NOAAPORT satellite ingestion systems also have access to GINI imagery. What set of GINI images they may get will depend on which NOAAPORT channels they receive. Unidata McIDAS users also have access to the NOAAPORT GINI imagery through ADDE.

NOAAPORT Channel 1 GINI imagery.

Imagery Data type ADDE dataset names
4 km 13.3 um East CONUS GINIEAST/GE8KCO2
4 km 3.9 um East CONUS GINIEAST/GE4K39
4 km 10.7 um East CONUS GINIEAST/GE4KIR
24 km 12.0 um Nhem-Composite GINIEAST/GNC24K12
24 km 3.9 um Nhem-Composite GINIEAST/GNC24K39
24 km 10.7 um Nhem-Composite GINIEAST/GNC24KIR
24 km VIS Nhem-Composite GINIEAST/GNC24KVIS
24 km WV Nhem-Composite GINIEAST/GNC24KWV
8 km 10.7 um Puerto Rico National GINIEAST/GPN8KIR
8 km VIS Puerto Rico National GINIEAST/GPN8KVIS
8 km WV Puerto Rico National GINIEAST/GPN8KWV
1 km VIS Puerto Rico Regional GINIEAST/GPR1KVIS
4 km 12.0 um Puerto Rico Regional GINIEAST/GPR4K12
4 km 3.9 um Puerto Rico Regional GINIEAST/GPR4K39
4 km 10.7 um Puerto Rico Regional GINIEAST/GPR4KIR
8 km WV Puerto Rico Regional GINIEAST/GPR8KWV
8 km 12.0 um Super-National GINIEAST/GSN8K12
8 km 3.9 um Super-National GINIEAST/GSN8K39
8 km Sounder Cloud Top Pressure GINIEAST/GSN8KCTP
8 km 10.7 um Super-National GINIEAST/GSN8KIR
8 km Sounder Lifted Index GINIEAST/GSN8KLI
8 km Sounder Precipitable Water GINIEAST/GSN8KPW
8 km Sounder SFC Skin Temperature GINIEAST/GSN8KSFCT
8 km VIS Super-National GINIEAST/GSN8KVIS
8 km WV Super-National GINIEAST/GSN8KWV

NOAAPORT Channel 2 GINI imagery.

Imagery Data type ADDE dataset names
8 km 10.7 um Alaska National GINIWEST/GAN8KIR
8 km VIS Alaska National GINIWEST/GAN8KVIS
8 km WV Alaska National GINIWEST/GAN8KWV
16 km WV Alaska Regional GINIWEST/GAR16KWV
2 km VIS Alaska Regional GINIWEST/GAR2KVIS
8 km 12.0 um Alaska Regional GINIWEST/GAR8K12
8 km 3.9 um Alaska Regional GINIWEST/GAR8K39
8 km 10.7 um Alaska Regional GINIWEST/GAR8KIR
14 km IR Hawaii National GINIWEST/GHN14KIR
14 km VIS Hawaii National GINIWEST/GHN14KVIS
14 km WV Hawaii National GINIWEST/GHN14KWV
1 km VIS Hawaii Regional GINIWEST/GHR1KVIS
4 km 12.0 Hawaii Regional GINIWEST/GHR4K12
4 km 3.9 um Hawaii Regional GINIWEST/GHR4K39
4 km 10.7 um Hawaii Regional GINIWEST/GHR4KIR
8 km WV Hawaii Regional GINIWEST/GHR8KWV
24 km 10.7 um Mult-Composite GINIWEST/GMC24KIR
24 km VIS Mult-Composite GINIWEST/GMC24KVIS
24 km WV Mult-Composite GINIWEST/GMC24KWV
24 km 12.0 um Nhem-Composite GINIWEST/GNC24K12
24 km 3.9 um Nhem-Composite GINIWEST/GNC24K39
24 km 10.7 um Nhem-Composite GINIWEST/GNC24KIR
24 km VIS Nhem-Composite GINIWEST/GNC24KVIS
24 km WV Nhem-Composite GINIWEST/GNC24KWV
8 km 12.0 um Super-National GINIWEST/GSN8K12
8 km 3.9 um Super-National GINIWEST/GSN8K39
8 km Sounder Cloud Top Pressure GINIWEST/GSN8KCTP
8 km 10.7 um Super-National GINIWEST/GSN8KIR
8 km Sounder Lifted Index GINIWEST/GSN8KLI
8 km Sounder Precipitable Water GINIWEST/GSN8KPW
8 km Sounder SFC Skin Temperature GINIWEST/GSN8KSFCT
8 km VIS Super-National GINIWEST/GSN8KVIS
8 km WV Super-National GINIWEST/GSN8KWV
4 km 12.0 um West CONUS GINIWEST/GW4K12
4 km 3.9 um West CONUS GINIWEST/GW4K39
4 km 10.7 um West CONUS GINIWEST/GW4KIR

NOAAPORT Channel 1/2 GINI imagery.

NOAAPORT GOES-East/West Composite GINI Imagery
Imagery Data type ADDE dataset names
24 km 12.0 um Nhem-CompositeGINICOMP/GNC24K12
24 km 3.9 um Nhem-Composite GINICOMP/GNC24K39
24 km 10.7 um Nhem-CompositeGINICOMP/GNC24KIR
24 km VIS Nhem-Composite GINICOMP/GNC24KVIS
24 km WV Nhem-Composite GINICOMP/GNC24KWV
8 km 12.0 um Super-National GINICOMP/GSN8K12
8 km 3.9 um Super-National GINICOMP/GSN8K39
8 km 10.7 um Super-National GINICOMP/GSN8KIR
8 km VIS Super-National GINICOMP/GSN8KVIS
8 km WV Super-National GINICOMP/GSN8KWV

Unidata sites can also subscribe to WSI Corporation for NIDS and NOWrad® imagery in non-AREA format.

WSI NIDS and NOWrad Imagery
Imagery Data type ADDE dataset names
NIDS Base Reflectivity Tilt 1 RTNIDS/BREF1
NIDS Base Reflectivity Tilt 2 RTNIDS/BREF2
NIDS Base Reflectivity Tilt 3 RTNIDS/BREF3
NIDS Base Reflectivity Tilt 4 RTNIDS/BREF4
NIDS Composite Reflectivity RTNIDS/CREF
NIDS Layer Reflect SFC-24 K ft RTNIDS/LREF1
NIDS Layer Reflect 24-33 K ft RTNIDS/LREF2
NIDS Layer Reflect 33-60 K ft RTNIDS/LREF3
NIDS Vertical Liquid H2O RTNIDS/VIL
NIDS 1-hour Surface Rain Total RTNIDS/PRE1
NIDS 3-hour Surface Rain Total RTNIDS/PRE3
NIDS Storm Total Rainfall RTNIDS/PRET
NIDS Radial Velocity Tilt 1 RTNIDS/RVEL1
NIDS Radial Velocity Tilt 2 RTNIDS/RVEL2
NIDS Radial Velocity Tilt 3 RTNIDS/RVEL3
NIDS Radial Velocity Tilt 4 RTNIDS/RVEL4
NIDS 248 nm Base Reflectivity RTNIDS/BRLR1
NIDS Storm-Rel Mean Vel Tilt 1 RTNIDS/SRMV1
NIDS Storm-Rel Mean Vel Tilt 2 RTNIDS/SRMV2
NOWrad 2 km US Composite Reflectivity RTNOWRAD/2KM
NOWrad 8 km US Composite Reflectivity RTNOWRAD/8KM

Unidata's History Data

The products in the Unidata-Wisconsin datastream are archived at SSEC for retrieval by Unidata sites. The archive contains data from 1991 to the present. A description of the archive and how to access it can be found on the Unidata home page under Data Recovery Information

Coordinate Systems

McIDAS references image data in four different, but interconnected coordinate systems:

Image Coordinates

The image coordinate system forms the basis for the other McIDAS coordinate systems. A full image is a sequence of lines and elements arranged from top to bottom. The top line and leftmost element have image coordinates (1,1). Therefore, each pixel has a unique pair of line and element values that are its image coordinates. The figure below represents a full image, image sector and displayed area. The upper-left image coordinates of the full image are (1,1) and the upper-left coordinates of the image sector are (3500,5000).

Area (File) Coordinates

Area coordinates (file coordinates in ADDE) are based on the size of the area only. Like image coordinates, area coordinates are referenced as lines and elements. The first pixel has area coordinates (0,0) as shown in the image sector below. The bottom-right pixel has area coordinates (LSIZ-1, ESIZ-1) where LSIZ and ESIZ are the number of lines and elements in the area.

Earth Coordinates

If the displayed image is navigated, the image coordinates can be converted to earth coordinates (latitude and longitude). Earth coordinates are specified in degrees, minutes, and seconds in the form DDD:MM:SS. Southern latitudes and longitude east of Greenwich are negative. Latitudes run from -90:00:00 to +90:00:00 and longitudes run from -180:00:00 to +180:00:00.

TV Coordinates

The pixels on the McIDAS image frames are arranged by raster lines and pictel elements. The raster lines run horizontally across the frame and the pictel elements run vertically across the frame. The pixel in the upper-left corner of the frame is numbered (1,1) which means (raster line 1, pictel element 1). The total number of raster lines and pictel elements on the frame is determined by the frame size. The lower-right corner of the default-sized frame is (480,640) in TV coordinates.

Image Navigation

Navigation, as applied to satellite imagery, means the conversion between satellite image coordinates (line and element) and earth coordinates (latitude and longitude). This is usually done when the data is ingested.

If a displayed image sector is navigated, McIDAS can convert the image coordinates of a specified pixel to earth coordinates. The E command lists the earth, TV and image coordinates at the cursor center.

Image Resolution

Image resolution is measured in kilometers and is highest at the subsatellite point. The highest available resolution depends on the satellite and image type:

This means that a single GOES infrared pixel at the subsatellite point represents a 4km x 4km square on the earth's surface, and a single METEOSAT visible pixel at the subsatellite point represents a 1 km x 1 km square on the earth's surface, etc. The further a pixel is located from the subsatellite point, the lower its resolution.

You can display imagery at a resolution other than that stored in the area. Specifying a positive magnification factor in McIDAS commands (e.g., IMGDISP) enlarges or blows up the data by replicating pixel values; a negative magnification factor produces a blow down by sampling pixel values. For example, if you choose a magnification factor of 16, the value of each pixel in the area is duplicated 256 times (in a 16 x 16 box of pixels) when displayed on the frame. If you choose a magnification factor of -4, the value of every fourth element along every fourth line is displayed as one pixel on the image frame.

Other Digital Imagery

Although geostationary satellites, polar orbiting satellites and radar images are usually displayed, you can digitize any data and display it on McIDAS. For example, cell proteins have been digitized for biochemistry studies and human photographs have been digitized to aid in forensic work.

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