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Sensor and Data Characteristics

General properties | Wavelengths | Spectral resolution | Spatial data cropping | Target spatial coordinates | Filename conventions | ENVI header files | Scale factor | Level 1B | Level 1BM | Geolocation | Flags | Level 2A | Additional products | Processing versions | NASA HDF5 files | NASA/OSU differences

IMPORTANT NOTE: The HICO data files provided by NASA differ in format from the HICO data files provided on this website. For more details see the NASA/OSU differences section below.

General properties

platform International Space Station (ISS)
HICO launch September 10, 2009
HICO installed on ISS September 24, 2009
first image date September 25, 2009
last image date September 13, 2014
HICO end of operations September 13, 2014
on-orbit lifetime one year minimum
orbit near circular (see the Orbit page)
inclination 51.6o
altitude 343 km (varies)
ISS orientation +XVV (standard forward orientation)
-XVV (reverse orientation - infrequent)
orbit repeat time 3 days (approximate)
orbit lighting cycle 63 days
orbit period 90 minutes
scenes per orbit 1 maximum
scenes per day 15 maximum
cross-track pointing varies from -45 to +30 degrees
-45: 45 degrees port (north if +XVV orientation)
+30: 30 degrees starboard (south if +XVV orientation)
swath orientation varies depending on the orbit path:
NW to SE (descending)
SW to NE (ascending)
ground sample distance (GSD) 90 m (varies with altitude and angle)
scene size (km) 42 x 192 km (varies with altitude and angle)
scene size (pixels) 500 x 2000 pixels (width x length) (details below)
(512 x 2000 pixels uncropped)
sensor field of view (FOV) 6.92o (i.e. +/- 3.46o from the center)
covering 512 cross-track pixels
wavebands 87 bands (details below)
(128 bands uncropped)
wavelengths 400 - 900 nm (details below)
(353 - 1080 nm uncropped)
RGB bands R : 638.9 nm (band 42)
G :
553.0 nm (band 27)
B : 461.4 nm (band 11)
spectral resolution 5.7 nm (details below)
spectral FWHM 10 nm (400 - 745 nm)
20 nm (746 - 900 nm)
(details below)
signal-to-noise ratio (SNR) > 200:1 for water-penetrating wavelengths and assuming 5% albedo
polarization sensitivity < 5% (430 - 1000 nm)
data format from this website: binary BIL and BSQ (ENVI™ compatible1)
from NASA: HDF5
disk space required per scene L1B: 120 MB (varies) / 230 MB (uncompressed)
L2A: 400 MB (varies) / 696 MB (uncompressed)

For more information, see: Lucke, R.L. et al. (2011), "Hyperspectral Imager for the Coastal Ocean: instrument description and first images", Appl. Opt. v 50(11), 1501-1516.

Wavelengths

The table below lists all 128 wavelengths collected by HICO. Only a subset of these wavelengths (the 87 bands from 400 - 900 nm; shown in blue) are included in the ENVI data files (provided on this website). The data from the remaining wavelengths (in grey) are less accurate. The HDF5 HICO files (from the NASA oceancolor website) include data from all of the wavelengths.

352.528
358.256
363.984
369.712
375.440
381.168
386.896
392.624
398.352
404.080
409.808
415.536
421.264
426.992
432.720
438.448
444.176
449.904
455.632
461.360
467.088
472.816
478.544
484.272
490.000
495.728
501.456
507.184
512.912
518.640
524.368
530.096
535.824
541.552
547.280
553.008
558.736
564.464
570.192
575.920
581.648
587.376
593.104
598.832
604.560
610.288
616.016
621.744

627.472
633.200
638.928
644.656
650.384
656.112
661.840
667.568
673.296
679.024
684.752
690.480
696.208
701.936
707.664
713.392

719.120
724.848
730.576
736.304
742.032
747.760
753.488
759.216
764.944
770.672
776.400
782.128
787.856
793.584
799.312
805.040
810.768
816.496
822.224
827.952
833.680
839.408
845.136
850.864
856.592
862.320
868.048
873.776
879.504
885.232
890.960
896.688
902.416
908.144
913.872
919.600
925.328
931.056
936.784
942.512
948.240
953.968
959.696
965.424
971.152
976.880
982.608
988.336

994.064
999.790
1005.52
1011.25
1016.98
1022.70
1028.43
1034.16
1039.89
1045.62
1051.34
1057.07
1062.80
1068.53
1074.26
1079.98

 

Spectral resolution

HICO provides data at 5.7 nm spectral resolution. Spectral data are originally collected at 1.9 nm resolution; to increase the signal to noise ratio, three bands are combined on the detector producing wavelength centers 5.7 nm apart. The resulting wavelengths are shown in the table above.

A smoothing filter (Gaussian) is applied to the uncalibrated spectral data to fix etaloning at the longer wavelengths. The size of the filter is 10 nm for the shorter wavelengths (400 - 745 nm) and 20 nm for the longer wavelengths (746 - 900 nm). Thus the data are 10 (or 20) nm width data centered on 5.7 nm wavelength centers. The filter sizes for each wavelength can be found in the header files accompanying the data, under the parameter name "fwhm".

 

Spatial data cropping

At some point during the transit and installation of HICO, the sensor physically shifted relative to the viewing slit. The edge of the viewing slit was visible in every scene. This effect has been removed in the ENVI HICO files by cropping each data file spatially to remove 10 pixels from the affected side of each scene. Two pixels were also removed from the opposite side. This reduces the width of each scene from 512 pixels to 500 pixels. Note that for scenes collected in the standard forward satellite orientation (+XVV), the affected side was the left side of the scene (as viewed in ENVI) (pixels 1-10). For the reverse orientation (-XVV) the affected side was the right side of the scene (pixels 503-512). This spatial cropping is performed on all of the different data types (hico.bil, rad_ndvi, rad_geom, rad_rgb, rad_flag, and LonLatViewAngles). Note that the HDF5 version of the files (from oceancolor.gsfc.nasa.gov) have not been cropped.

 

Target spatial coordinates

Multiple scenes from the same target do not cover identical spatial coordinates. This is due to a number of reasons outlined below.

Targeting is NOT (and in fact for HICO cannot be) determined based on ISS attitude and position at the instant of image acquisition.  Targeting is determined from hours to days ahead of time using a predicted ISS ephemeris and a predicted mean-attitude (i.e., the Torque Equilibrium Attitude -TEA).  Therefor, changes in the ephemeris, oscillations about the TEA, and time precision and offset issues can affect the center coordinates of each collected scene in both the along-track and cross-track directions. In some cases, the resulting spatial offset can be more than 10 km.

Changes in the ISS altitude can also affect the target spatial coverage by varying the pixel size. Atmospheric drag gradually decreases the altitude. Periodic reboosts are performed to compensate for the loss in altitude. Altitude changes are also frequently made by the ISS during docking maneuvers.

The HICO pointing angle (the angle HICO is tilted to the side to view the target) also affects the pixel size. HICO can vary its pointing angle from -45 degrees to +30 degrees. Looks at 20 degrees (for example) have larger pixel sizes than looks at nadir. When the ISS is travelling in its standard forward mode (+XVV), negative pointing angles are to the north and positive angles are to the south. The opposite is true when travelling in -XVV mode.

On rare occasions the ISS orientation is temporarily changed from its standard forward +XVV mode to the reverse -XVV mode (flying backwards). This orientation change usually happens during shuttle docking maneuvers. During the first year of HICO operations, the targeting calculations were incorrect for this infrequent -XVV mode, and the scenes in this mode were collected from the wrong places. The ISS orientation is listed in the header file.

 

Filename conventions

ENVI files (this website)

Some examples of HICO filenames are:

iss.2010018.0118.182518.L1B.CCNY.v03.1689.20100119130950.100m.hico.bil
iss.2010018.0118.182518.L2A.CCNY.v03.1689.20100119130950.100m.hico_NLsf.hdr

They follow the convention in the table below.

iss.YYYYDDD.mmdd.HHMMSS.L*.target.v*.sceneID.YYYYmmddHHMMSS.100m.hico*
iss HICO platform name
YYYYDDD.mmdd.HHMMSS collection datetime in UTC (year, day of year, month, day of month, hour, minute, second)
L* processing level (L1B, L2A, ...)
target target name (e.g. Monterey_Bay_CA)
v* processing version for the L1B data (v03, ...)
sceneID unique scene ID (e.g. 1244)
YYYYmmddHHMMSS datetime that the raw (level 0) file was created in UTC (year, month, day of month, hour, minute, second)
100m approximate scene spatial resolution
hico* the file type (e.g. hico.bil, hico.hdr, hico_refl.bil, ...)

HDF5 files (NASA oceancolor website)

An example NASA HDF5 HICO filename is:
H2013020173455.L1B_ISS

They follow the convention in the table below.

HYYYYDDDHHMMSS.L*_ISS
H HICO
YYYYDDDHHMMSS collection datetime in UTC (year, day of year, hour, minute, second)
L* processing level (L1B, L2A, ...)
ISS HICO platform name

 

 

ENVI header files

Every ENVI HICO data file is accompanied by an ASCII header (*.hdr) file compatible with ENVI software1. This file contains information about the data file format; key parameters are listed in the table below. For more information see the section "The ENVI Header Format" of the Getting Started with ENVI manual. In addition, the header files contain a wealth of other HICO-specific information about the scene including processing details, wavebands, units, and more (see the sample header file).

samples number of samples per line (width of scene in pixels)
lines number of lines per band (height of scene in pixels)
bands number of bands
header offset offset in bytes from the start of the file until the data starts
data type 1 = 8-bit byte
2 = 16-bit signed integer
4 = 32-bit floating point
interleave interleave type (the order the data are stored):
bil (Band Interleaved by Line)
bsq (Band Sequential)
byte order the order the bytes are stored (least significant or most significant first)
0 = little-endian (LSF)
1 = big-endian (MSF)
x start The coordinate for the upper-left hand pixel in the image. Since the HICO data have been spatially cropped at OSU, this value is not 1. Rather, it is 11 for scenes collected in +XVV satellite orientation, and 3 for those from -XVV orientation.
wavelength an array of the center wavelengths
fwhm an array of the spectral width of each waveband
scene_id the unique numeric scene ID
image_center_date scene center date in UTC (year, month, day)
image_center_time scene center time in UTC (hour, minute, second)
image_center_long scene center longitude in decimal degrees (0 - 180)
image_center_long_hem longitude hemisphere: E (east) or W (west)
image_center_lat scene center latitude in decimal degrees (0 - 90)
image_center_lat_hem latitude hemisphere: S (south) or N (north)
image_center_zenith_ang scene center zenith angle (decimal degrees)
image_center_azimuth_ang scene center azimuth angle (decimal degrees)
sensor_altitude altitude (km)
image_scale_factor the data must be divided by this scale factor to transform them to the appropriate units
target_name the target name
target_angle HICO sensor view angle ranging from 15 to 90 degrees (60 degrees is pointing straight down). This can be converted to the HICO pointing angle by subtracting 60, resulting in a range of -45 to 30 degrees.
target_aos scene acquisition of signal (AOS) date and time in UTC

 

Scale factor

The user must apply a scale factor to all radiance data to transform them to appropriate units.

For ENVI Level 1b data, the scale factor is listed in the accompanying header file under the parameter name "image_scale_factor". The data in the ENVI Level 1b file must be divided by the image_scale_factor before use. For Level 1b data the factor is currently 50.

For HDF5 Level 1b data, the scale factor is in the Metadata-Variable_Attributes-products/Lt-slope parameter. The data in the HDF5 Level 1b file must be multiplied by the slope before use. For Level 1b data the slope is currently 0.02.

For ENVI Level 2 data, the scale factors can be found in the accompanying header files under the parameter name "tafkaa_output_scale_factor". The data in the Level 2 file must be divided by the tafkaa_output_scale_factor before use. The scale factor varies for each type of Level 2 file.

Why is there a scale factor at all?
By scaling the data they can be stored more efficiently in the data file. For example, by multiplying the Level 1b radiances by 50, it is possible to store the data as two-byte signed integers.

Level 1B: calibrated radiances with geolocation

Processing from level 0 (raw data) to level 1b includes dark current subtraction, CCD smear correction, 2nd order correction, spectral calibration and radiance calibration. Note that a scale factor must be applied to all radiance data before use.

The following table lists all of the file types associated with the main ENVI Level 1b file.

File Type File size Array size Data Type Interleave
hico.bil The main data file containing a hyperspectral image cube of top-of-the-atmosphere radiances (400 - 900 nm) (W m-2 µm-1 sr-1)
  174 MB 2000 x 500 x 87 16-bit signed integer BIL
rad_geom Navigation information (see the Geolocation section for important information) (latitude, longitude, view zenith, view azimuth, solar zenith, solar azimuth) (degrees)
  24 MB 2000 x 500 x 6 32-bit floating point BIL
rad_rgb A truecolor RGB image cube (wavebands 461.4, 553.0, and 638.9 nm) (dimensionless)
  3 MB 2000 x 500 x 3 8-bit byte BSQ
rad_ndvi Vegetation indices (not atmospherically corrected). Uses wavebands at 869 and 668 nm.
  12 MB 2000 x 500 x 3 32-bit floating point BSQ
rad_flag Quality flags (see flags section below).
  1 MB 2000 x 500 x 1 8-bit byte BSQ
*.hdr Metadata for each of the above files. There is one hdr file for every BIL or BSQ file.
  8 kB N/A ascii N/A


Level 1BM: merged calibrated radiances

During the transmission of data from the satellite to earth, data packets are frequently lost. In those cases, multiple transmissions of the same data set are sometimes requested. The scene is then re-created by merging the different transmission files to reduce the number of drop-outs. The "L1BM" designates these files as "merged" files, unlike "L1B" files that arrived in a single transmission.

The very first file transmitted is designated "L1B". If it contains drop-outs, subsequent transmissions are made and merged with the first, creating L1BM files, and the L1B file is deleted. Usually the final transmission is drop-out free - if so, it is kept instead of the L1BM file (and is designated "L1B"). Files containing dropouts are usually a result of being unable to retransmit the file.

 

Geolocation

Currently, the NASA HDF5 HICO files contain better geolocation data than the ENVI files available from this website. The NASA files are available from the NASA Ocean Color website with an EOSDIS user account.

The ENVI HICO data (available from this website) arrive with only rough geolocation information in accompanying files called rad_geom. Work is in progress at NRL to improve the geolocation information in these files.

Detailed instructions on geolocating ENVI HICO scenes can be found on the "Geolocating the Data" page.

 

Flags

Some rough data quality flags are provided in the Level 1b rad_flag files. There are eight flags, stored together as one byte per pixel (one flag per bit). Flags have a value of zero if they are not set (false), otherwise they are one (true). In the table below, the bit positions assume little-endian bit order (least significant bit is bit 0).

Bit Flag Description
0 1 LAND land (or possibly glint or clouds)
NIR > 0.02)
1 2 NAVWARN latitude or longitude out of bounds
2 3 NAVFAIL navigation is rough (currently always set to 1)
3 4 HISATZEN satellite view angle > 60o
4 5 HISOLZEN solar zenith angle at estimated position > 75o
5 6 SATURATE pixel has ≥ 1 saturated bands
6 7 CALFAIL pixel has ≥ bands from a dropped packet
7 8 CLOUD rough cloud mask
NIR > 0.05 and ρRED > 0.5) or (0.8 < ρNIRRED < 1.1)

An example is illustrated in the table below.

Flag example
ASCII value 79
Bit number 7 6 5 4 3 2 1 0
Flag 8 7 6 5 4 3 2 1
Binary 79 0 1 0 0 1 1 1 1
The flags set are LAND, NAVWARN, NAVFAIL, HISATZEN, and CALFAIL.

 

Level 2A : atmospherically corrected remote sensing reflectances

Note: Only a small set of Level 2A scenes are currently available. Level 2A scenes are currently produced on an as-needed basis. Atmospherically corrected scenes may be requested by contacting Curt Davis.

Numerous atmospheric correction methods exist. The HICO team researchers at NRL and OSU are investigating the optimum method to use with HICO data. The small set of Level 2A files currently available are a result of some of these first attempts.

One of the methods currently used at Oregon State University employs a modified version of Tafkaa_6s (Atmospheric Correction Algorithm for the Land)1. The modification adds water vapor correction at 825 nm to improve retrievals over coastal areas. The Level 2A files provided on this website were all derived using this method.

Note that scale factors need to be applied to the data to convert the data to appropriate units. The scale factors can be found in the accompanying header files under the parameter name "tafkaa_output_scale_factor". The data must be divided by this scale factor before use.

The types of files created with this method follow below.

File Type File size Array size Data Type Interleave
arfl apparent at-sensor reflectance (dimensionless)
(not atmospherically corrected, only geometric)
  174 MB 2000 x 500 x 87 16-bit signed integer BIL
refl surface reflectance (dimensionless)
  174 MB 2000 x 500 x 87 16-bit signed integer BIL
R_rs surface remote sensing reflectance (1/sr)
  174 MB 2000 x 500 x 87 16-bit signed integer BIL
NLsf normalized ground (water) leaving radiance (W m-2 µm-1 sr-1)
  174 MB 2000 x 500 x 87 16-bit signed integer BIL
*.hdr Metadata for each of the above files. There is one hdr file for every BIL or BSQ file.
  15 kB N/A ascii N/A

The inputs used for Tafkaa are recorded in the accompanying header files under the parameter names "tafkaa*". Some of the typical parameters and their options include:

Atmospheric Model Tropical
Mid-Lat Summer
Mid-Lat Winter
Sub-Artic Winter
US Standard 1982
Ozone Amount 0.3400
Selected Gases H20 03 N20 02
Aerosol Model None
Continental
Maritime
Urban
User Specific Basic Components
Desertic
Biomass Burning
Stratospheric
Aeronet Inversion Data
Aerosol Visibility -1 (none)
0 - 299 km
Water Vapor Line 1 0.7050 (3) 0.7250 (5) 0.7450 (3)
Water Vapor Line 2 0.8050 (3) 0.8250 (5) 0.8450 (3)

 

Additional products on request

  • Level 2B standard data products:
    • a set of MODIS-type products (chl, suspended sediments, CDOM, IOPs, etc.). HICO channels are spectrally binned to create simulated MODIS data at 90 m GSD (as opposed to the 1 km MODIS GSD).
  • other requests will be considered on a case by case basis

Processing versions
last updated March 28, 2012

    Date implemented Dates reprocessed
v04 4.00.00 March 15, 2012 Jan 1, 2010 - ongoing
v03 3.00.10    
  3.0.7    
  3.0.3    
  3.0.1    
  3.0.0    

version 4.00.00

The differences between v03 (3.00.10) and v04 (4.00.00) follow:

  1. The dark algorithm has been updated to despike the pre- and post-dark data.  In addition, the dark algorithm now uses a temperature-dependent coefficient which controls how fast the dark value is expected to increase during imaging.
  2. The wavelengths and their calibration files have been updated.  The wavelengths have all shifted slightly (for example, 404.980 nm (v03) is now 404.080 nm (v04)).  Data quality is still suspect outside of the 400-900 nm range.

NASA HDF5 files

The main HICO website (this site) provides data in the original ENVI HICO format. In January 2013, NASA began funding the HICO project and providing data to the public from the NASA Ocean Color website. NASA provides the data in HDF5 format to conform with the other ocean color satellite data that they manage. No wavelength or pixel cropping is done to these HDF5 files. Currently only Level 1B data are available.

The NASA HDF5 HICO data are freely available to the public, however an EOSDIS user account is required to access the data. To register for an account, please visit: https://earthdata.nasa.gov/urs/register.

The NASA Level 1B HDF5 files contain the datasets listed in the table below.

products
Lt top of atmosphere radiance (W/m2/um/sr)
  2000 x 512 x 128 16-bit unsigned integer
images
true_color true color (638.9, 553.0, 461.3 nm)
  2000 x 512 x 3 8-bit unsigned character
navigation
latitudes latitude (degrees N)  
  2000 x 512 32-bit floating point
longitudes longitude (degress E)  
  2000 x 512 32-bit floating point
sensor_azimuth sensor azimuth (degrees)  
  2000 x 512 32-bit floating point
sensor_zenith sensor zenith (degrees)  
  2000 x 512 32-bit floating point
solar_azimuth solar azimuth (degrees)  
  2000 x 512 32-bit floating point
solar_zenith solar zenith (degrees)  
  2000 x 512 32-bit floating point
quality
flags scan-line quality flags  
  2000 x 512 8-bit unsigned character
data    
The "hico" dataset below was accidentally included in some of the earlier files. It is absent from more recent files.
hico Level 0 data (W/m2/um/sr)
  2000 x 512 x 128 16-bit unsigned integer

NASA/OSU differences
information updated August 5, 2014

The differences between the HICO data provided by the main HICO website (this website, maintained at Oregon State University) and the data provided on the NASA Ocean Color website follow in the table below. Please visit the links within the table for additional information.

  HICO website NASA Ocean Color
Data access webpage Search Data Level 1 & 2 browser
Account type required none EOSDIS
File format ENVI HDF5
Filename convention iss* H*_ISS
Wavelengths provided 400 - 900 nm 350 - 1080 nm
Data edges cropped yes no
Geolocation quality good better
Number of targets available all all

 

 

 




1 Software products listed on this webpage are not meant to imply endorsement by the HICO team, the Office of Naval Research, or NASA. The products named are provided only as examples of software that may be used.

 

 
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  Website Administrator: Jasmine Nahorniak
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