Warren,1981).For water and ice surfaces, this corresponding error is smaller than 
0.1 C and can be neglected. Young ice surfaces remain wet due to high salinity | the 
as shown by ground measurements at the Resolute Passage ice station. Consequent- = stat 
ly brightness temperature measurements of sea ice up to 30 cm thick were correc- | temp 
ted with the emissivity of water. For true surface temperature, the brightness ref] 
temperature has to be corrected to compensate for emssivity and for cosine de: infr 
pendency of the emissivity (Fig.2) ing 
  
Figure 2: Temperature correction ar 
AT, fon vertical PRT-5 (9.5 £o ot : ] 
11.5 gum) measurements of water, 
. SE SEA -ICE (dry) ~ 7 
Âce and snow surfaces do com- ; = Marca ii t 
. me Ce sh N z | 
pensate (or emsstvittes. ee | pus 
clou 
  
  
  
  
  
  
Topy=brightness temperature at SEA -ICE (ve) = set 
T. = "true" temperature ar ATT, Tp 4 and 
T u ] diti 
EUR Ur TEE TR | Fig 
AR j- | clou 
——— the 
Figu 
ABSORPTION AND EMISSION: The temperature correction (AT_) necessary to 
compensate for water vapour absorption and emission of an atmospheric layer bet- 
ween aircraft and ground was also calculated. This temperature correction for 
absorption and emission can be expressed in the following manner: 
kau(E(T )-E(T)) 
AT, se" 
dE(T )/dT 
where k is the average absorptivity of water vapour in the given spec- 
tral range, and E(T_) and E(T.) the energies of black body radiations at air 
temperature T and Surface temperture T . For the calculation of the optical 
path au, the air column at saturation was taken. The deviation of temperature 
corrections of an air layer with only 70% humidity is 0.1 C or higher for air 
temperatures above freezing point and surface temperatures below -30 C (upper 
left corner , Fig.3). Suchextreme situations never occured during the winter 
remote sensing missions, 1980/81. 
Figure 3: Temperature corrections M37 
AT to compensate for absorption a | 
and emission of atmospheric wa- ves atr A 1,2 
ten vapour for a flying altitude ; | 
of 300 m. A 
Tppy-bréghtness temperature "eL. Ye 
T = "true" surface temp. | 
T = air temperature at flight + 
a ob 
Level "ar ATUS Tu. e 
| ws obte 
——— m | fmm 
  
  
Tour OO 
770