Processing/BrightnessTemperature: t_bb.pro

File t_bb.pro, 5.3 KB (added by peland, 17 years ago)

calculates black body temperature as a function of radiance from a lookup table

Line 
1function t_bb,radiance,lambda,response,emissivity=eps,range=range, $
2  t_bb_data=t_bb_data,autorange=autorange,truncate=truncate,spline=spline, $
3  verbose=verbose
4
5; calculates temperature (K) corresponding to given radiance (W/m2/sr/um) from
6; instrument with response curve response(lambda) (lambda in nm, response
7; relative) and optional emissivity eps (default 1) - lookup table calculated
8; and returned in structure t_bb_data for future use if multiple calls are
9; required. If a temperature range for the lookup table different from the
10; default is required, it can be specified using range=[t_min,t_max[,t_step]]
11; though the program will attempt to autorange if required.
12
13default_t_min=270. ; minimum lookup table temperature
14default_t_max=370. ; maximum lookup table temperature
15default_t_step=.1  ; lookup table temperature step
16max_n_t=5000       ; maximum number of lookup table entries (for autoranging)
17n_non_spline_tags=10 ; number of tags in t_bb_data excluding spline
18auto=keyword_set(autorange)
19chop=keyword_set(truncate)
20spline_set=keyword_set(spline)
21verb=keyword_set(verbose)
22n_lambda=n_elements(lambda)
23n_eps=n_elements(eps)
24if n_eps gt 1 && n_eps ne n_elements(radiance) then $
25  message,'T_BB: Emissivity must match radiance'
26if n_elements(response) ne n_lambda then $
27  message,'T_BB: Response must have same number of elements as lambda'
28n_range=n_elements(range)
29range_set=n_range gt 0
30t_bb_data_present=n_elements(t_bb_data) gt 0
31if range_set then begin
32  if n_range lt 2 then message,'T_BB: Range must have at least 2 elements'
33  t_min=range[0]
34  t_max=range[1]
35  if n_range gt 2 then t_step=range[2] else t_step=default_t_step
36endif else if t_bb_data_present then begin
37  t_min=t_bb_data.t_min
38  t_max=t_bb_data.t_max
39  t_step=t_bb_data.t_step
40endif else begin
41  t_min=default_t_min
42  t_max=default_t_max
43  t_step=default_t_step
44endelse
45min_radiance=min(radiance,max=max_radiance)
46if t_bb_data_present then begin
47  too_low=min_radiance lt t_bb_data.rad_min
48  too_high=max_radiance gt t_bb_data.rad_max
49  if too_low || too_high then begin
50    if auto then begin
51      if too_low then begin ; expand downwards
52        t_min=t_min-.5*(t_max-t_min)>(.5*t_min)
53        t_bb_data_present=0
54      endif
55      if too_high then begin ; expand upwards
56        t_max=t_max+.5*(t_max-t_min)
57        t_bb_data_present=0
58      endif   
59      if verb then print,'Expanding T range to ',t_min,t_max
60    endif else if chop then begin ; truncate radiance to table limits
61      radiance=radiance>t_bb_data.rad_min<t_bb_data.rad_max
62    endif else message,'Lookup table radiance range: '+ $
63      string(t_bb_data.rad_min)+string(t_bb_data.rad_max)+', data: '+ $
64      string(min_radiance)+string(max_radiance)
65  endif
66endif
67if t_bb_data_present then begin
68  if range_set then if t_bb_data.t_min ne t_min || t_bb_data.t_max ne t_max $
69    || t_bb_data.t_step ne t_step then t_bb_data_present=0
70  if spline_set && n_tags(t_bb_data) le n_non_spline_tags then $
71    t_bb_data_present=0 ; splines requested but not found in table
72  if t_bb_data.n_lambda ne n_lambda then t_bb_data_present=0 else $
73    if max(t_bb_data.lambda ne lambda) || max(t_bb_data.response ne response)$
74    then t_bb_data_present=0
75  if ~t_bb_data_present then print,'T_BB WARNING: overwriting t_bb_data'
76endif
77if ~t_bb_data_present then begin ; set up t_bb_data
78  repeat begin
79    n_temps=floor((t_max-t_min)/t_step)+1
80    if auto && n_temps gt max_n_t then begin
81      n_temps=max_n_t
82      t_step=(t_max-t_min)/(n_temps-1)
83      if verb then print,'T_BB WARNING: changing t_step to ',t_step
84    endif
85    temps=t_min+findgen(n_temps)*t_step
86    radiances=l_band(lambda,response,temps)
87    rad_min=min(radiances,max=rad_max)
88    too_low=min_radiance lt rad_min
89    too_high=max_radiance gt rad_max
90    if too_low || too_high then begin
91      if auto then begin
92        if too_low then t_min=t_min-.5*(t_max-t_min)>(.5*t_min) ;expand downward
93        if too_high then t_max=t_max+.5*(t_max-t_min) ; expand upward
94        if verb then print,'Expanding T range to ',t_min,t_max, $
95          ', lookup table radiance range: ',rad_min,rad_max
96      endif else if chop then begin ; truncate radiance to table limits
97        radiance=radiance>rad_min<rad_max
98        too_low=0
99        too_high=0
100      endif else message,'Lookup table radiance range: '+string(rad_min)+ $
101        string(rad_max)+', data: '+string(min_radiance)+string(max_radiance)
102    endif
103  endrep until ~(too_low || too_high)
104  if spline_set then begin
105    spline=spl_init(radiances,temps)
106    t_bb_data={t_bb_str_spline,n_lambda:n_lambda,lambda:lambda, $
107      response:response,t_min:t_min,t_max:t_max,t_step:t_step,temps:temps, $
108      radiances:radiances,rad_min:rad_min,rad_max:rad_max,spline:spline}
109  endif else begin
110    t_bb_data={t_bb_str,n_lambda:n_lambda,lambda:lambda,response:response, $
111      t_min:t_min,t_max:t_max,t_step:t_step,temps:temps,radiances:radiances, $
112      rad_min:rad_min,rad_max:rad_max}
113  endelse
114endif
115if n_eps gt 0 then begin
116  if spline_set then return,spl_interp(t_bb_data.radiances,t_bb_data.temps, $
117    t_bb_data.spline,radiance/eps) else $
118    return,interpol(t_bb_data.temps,t_bb_data.radiances,radiance/eps)
119endif else begin
120  if spline_set then return,spl_interp(t_bb_data.radiances,t_bb_data.temps, $
121    t_bb_data.spline,radiance) else $
122    return,interpol(t_bb_data.temps,t_bb_data.radiances,radiance)
123endelse
124
125end