NAVCALC

Calculates satellite subpoints and orbit times.

Formats

NAVCALC navdataset option [keywords]
NAVCALC imgdataset option [keywords]
NAVCALC tledataset option [keywords]

Parameters

navdataset	name of the ADDE dataset containing the system navigation files for a satellite; specify as group/descriptor or alias
imgdataset	name and position of the ADDE dataset containing the image to use as a navigation source; specify as group/descriptor.position or alias.position; when specifying an image dataset, you must also use the TYPE=I keyword (position default=0)
tledataset	name of the ADDE dataset containing the NORAD Two-Line Element (TLE) data; specify as group/descriptor or alias; when specifying a TLE dataset, you also must use the TYPE=T keyword
option	FWD	computes the earth coordinates of a surface point based on image coordinates; not valid with TLE datasets
	HGT	estimates the height of a feature based on earth coordinates and image coordinates; not valid with TLE datasets
	INV	computes the image coordinates of a surface point based on earth coordinates; not valid with TLE datasets
	LOS	computes the time ranges when a polar orbiting satellite is visible (in the line of sight) from a surface point
	SP	computes a geostationary satellite subpoint for a specific time; or computes polar orbiting satellite subpoints for a range of times
	VIEW	computes the times that a polar orbiting satellite and sensor view a surface point; not valid with TLE datasets

Keywords

ANTenna=	angle	minimum angle, in degrees, above the horizon at which a satellite signal is readable; valid only with the LOS option (default=5)
DAY=	bday eday	range of days for calculations; see the Remarks (default=current, or from imgdataset)
ELEInc=	inc num	increment between elements and the number of element values for multiple calculations using the FWD option
HEight=	height, in kilometers, of the surface point; valid only with the FWD, INV, LOS, and VIEW options (default=0 if the LATLON keyword is used to specify surface point; station height if the STATION keyword is used)
HTol=	height tolerance, in kilometers, for HGT option (default=0.5)
IMC=	ON	compute subpoint using navigation that has been corrected by the Image Motion Compensator; this keyword is valid only when using the SP option with GVAR (GOES-8 and later) image datasets (default)
	OFF	compute actual subpoint, ignoring the IMC
LATInc=	inc num	increment between latitudes and the number of latitude values for multiple calculations using the INV option
LATlon=	lat lon	earth coordinates of the surface point; valid only with the HGT, INV, LOS, and VIEW options
LINEle=	lin ele	image coordinates of the surface point; valid only with the FWD and HGT options
LINInc=	inc num	increment between lines and the number of line values for multiple calculations using the FWD option
LONInc=	inc num	increment between longitudes and the number of longitude values for multiple calculations using the INV option
SENsor=	type
	POES options:	AVHRR (default), HIRS, MSU
	DMSP options:	OLS (default), SSM/I, SSM/T, or SSM/T2
	GOES and GVAR options:	IMAGER (default) and SOUNDER
	this keyword is not valid with the SP option
STAtion=	station ID of the surface point; valid only with the HGT, INV, LOS, and VIEW options; specify as the ID, e.g., KMSN or YSSY, optionally followed by the station type in brackets, e.g., ARX[N] or ARX[V]; see the TYPE keyword in the STNLIST command for valid station types
TIME=	btime etime inc	time range for calculations and interval between subpoint calculations; see the Remarks (default=0 23:59:59, or from imgdataset; inc default=etime minus btime)
TYPE=	S	uses the system navigation files specified with navdataset (default)
	I	uses the navigation of the image specified with imgdataset; overrides the SENSOR keyword
	T 'sat'	uses the navigation of the TLE dataset specified in tledataset; sat is the name of the satellite in the dataset whose data you want to list; use the READ command to list the dataset and see which satellite names it contains

Remarks

Use both the DAY and TIME keywords to specify the time period for navigation calculations. For example, DAY=182 183 TIME=21 3 specifies a range from 21:00 UTC on day 182 through 03:00 UTC on day 183.

Specify inc with TIME keyword only when using the SP option with polar orbiting satellites. The SP option does not list day or time ranges for geostationary satellite navigation.

When selecting a portion of an image using the TIME keyword, specified earth or image coordinates must be present in that portion. When selecting a portion of a navigation file, specified or computed image coordinates are redefined based on that portion and not the entire file. For example, if a navigation file starts at 0 UTC but you specify TIME=6, the image coordinates 1,1 refer to the line starting at 6 UTC.

The LOS and VIEW options may not list the same number of entries: a satellite may be visible from the surface point, but not able to view the point.

The FWD option computes the earth coordinates of the northwest corner of a pixel. The INV option computes the image coordinates of a pixel containing the specified earth coordinates. Therefore, a NAVCALC INV command followed by a NAVCALC FWD command may not return the initial earth coordinates.

When working with GVAR system navigation files, navigation may not be from the time specified. NAVCALC requests navigation at the time specified with the TIME keyword. If navigation exists for that time or for earlier on that day, it is used. If not, NAVCALC requests navigation for six hours later, or 23:59:59, whichever is earlier. This request is repeated, advancing by six hours each time, until navigation is found or the end of the day is reached, meaning no navigation exists for that day.

The table below shows the meanings of column labels that appear in NAVCALC output for the FWD, HGT, and INV options.

Column Label	Description
hgt	Height of the given point.
sat	Zenith angle of the satellite from the given point.
solar	Zenith angle of the sun from the given point. If the sun is below the horizon for the given image and point, the solar and relaz values are "- - - - -".
relaz	Relative azimuth angle between the sun and the satellite, as seen from the given point. If the sun is behind the satellite, the relative azimuth is zero. If the sun is to the right, the relative azimuth is positive. If the given point is within 0.01 degree of the satellite subpoint, the relaz value is "undef" (undefined).

Examples

NAVCALC NAV/GOES8 SP DAY=96300

This entry lists the subpoint of the GOES-8 satellite on day 96300.

NAVCALC NAV/MODIS SP TYPE=T 'TERRA' TIME=12 15 :02

This entry lists the subpoints of the TERRA satellite every two minutes between 12 and 15 UTC of the current day.

NAVCALC NAV/NOAA12 VIEW LATLON=49 100.5 DAY=97001 97005

This entry lists the dates and times between 0:00 UTC on day 97001 and 23:59:59 UTC on day 97005 that the location 49° N, 100.5° W is in the view of the NOAA-12 satellite's AVHRR sensor.

NAVCALC A/A.8016 LOS TYPE=I STATION=KIRK TIME=18 12 DAY=93216 93219 ANTENNA=3

This entry lists the dates and times between 18 UTC on day 93216 and 12 UTC on day 93219 that the polar orbiting satellite with image data in position 8016 of dataset A/A is visible from an antenna in Kirksville, MO tracking at an angle of three degrees or greater above the horizon.

NAVCALC WALLOPS/N12HRPT.10 INV TYPE=I LATLON=43:08 89:21 HEIGHT=1

This entry computes the image line and element based on the specified latitude, longitude and height information, and the navigation of the image in position 10 of dataset WALLOPS/N12HRPT.

NAVCALC WALLOPS/N12HRPT.10 FWD TYPE=I LINELE=1223 1758 HEIGHT=1

This entry computes the latitude and longitude based on the specified line, element and height information, and the navigation of the image in position 10 of dataset WALLOPS/N12HRPT.

NAVCALC EAST/CONUSV.-2 HGT LINELE=3916 13436 LATLON=43:07:18 89:20:42 TYPE=I

This entry estimates the height of a feature based on its line, element, latitude and longitude information, and the navigation of the image in relative position -2 of dataset EAST/CONUSV.

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