Read File downloaded from ASTER data base. — read_ASTER

Reads and parses the header of a test file as available through the ASTER reflectance database. The Name field is retrieved and copied to attribute "what.measured". The header of the file is preserved as a comment.

Usage

read_ASTER_txt(
  file,
  date = NULL,
  geocode = NULL,
  label = NULL,
  tz = NULL,
  locale = readr::default_locale(),
  npixels = Inf
)

Arguments

file: character string
date: a POSIXct object to use to set the "when.measured" attribute. If NULL, the default, the date is extracted from the file header.
geocode: A data frame with columns lon and lat used to set attribute "where.measured".
label: character string, but if NULL the value of file is used, and if NA the "what.measured" attribute is not set.
tz: character Ignored.
locale: The locale controls defaults that vary from place to place. The default locale is US-centric (like R), but you can use locale to create your own locale that controls things like the default time zone, encoding, decimal mark, big mark, and day/month names.
npixels: integer Number of pixels in spectral data.

Value

A raw_spct object.

Note

The header in these files has metadata information, but mostly on the origin of the data. For a date and/or geocode are to be added to the return object it must be supplied by the user. as well as the date-time. Some metadata is extracted and added as attributes, while the whole header is copied to the comment attribute.

References

https://speclib.jpl.nasa.gov

Baldridge, A.; Hook, S.; Grove, C. & Rivera, G. (2009) The ASTER spectral library version 2.0. Remote Sensing of Environment. 113, 711-715

Examples


 file.name <- 
   system.file("extdata", "drygrass-spectrum.txt", 
               package = "photobiologyInOut", mustWork = TRUE)
                
 fred.spct <- read_ASTER_txt(file = file.name, npixels = Inf)
 
 fred.spct
#> Object: reflector_spct [2,559 x 2]
#> Wavelength range 380.49-14011 nm, step 0.8-38 nm 
#> Label: Name: Dry grass
#> File: drygrass-spectrum.txt 
#> Variables:
#>  w.length: Wavelength [nm]
#>  Rfr: Total spectral reflectance [/1] 
#> --
#> # A tibble: 2,559 × 2
#>    w.length   Rfr
#>       <dbl> <dbl>
#>  1     380. 0.142
#>  2     383. 0.143
#>  3     385. 0.145
#>  4     388. 0.147
#>  5     390. 0.148
#>  6     393. 0.150
#>  7     395. 0.153
#>  8     398. 0.154
#>  9     400. 0.157
#> 10     403. 0.159
#> # ℹ 2,549 more rows
 getWhatMeasured(fred.spct)
#> [1] "Name: Dry grass\nFile: drygrass-spectrum.txt"
 cat(comment(fred.spct))
#> ASTER database file 'drygrass-spectrum.txt' imported on 2025-03-10 15:48:17.254473 UTC
#> Name: Dry grass
#> Type:  Vegetation
#> Class:  Grasses
#> Subclass:  Dry grass
#> Particle Size:  Solid
#> Sample No.:  drygrass.doc
#> Owner:  JHU
#> Wavelength Range:  All
#> Origin:  The entire spectral range was measured at Johns Hopkins University.
#> Description:  Dry grass.  Spectra were assembled from two segments; the 
#> bidirectional VNIR and SWIR comprising segment one, and the hemispherical 
#> MWIR and TIR comprising segment two. The VNIR/SWIR spectrum was 
#> measured in the laboratory at JHU with a GER IRIS Mark IV, using a large piece 
#> of sod.  The grass was illuminated from directly above and measured at a 
#> reflectance angle of 60 degrees to avoid viewing the thatch. 
#> Measurement:  Bidirectional and directional hemispherical reflectance. 
#> First Column:  X
#> Second Column:  Y  
#> X Units:  Wavelength (micrometers)
#> Y Units:  Reflectance (percent)
#> First X Value: 0.38049
#> Last X Value: 14.011 
#> Number of X Values: 2559
#> Additional Information:  None.
#>