specificity) time constant of order tens and hundreds of milliseconds that prevents
high space resolution. It is mentioned for comparison that the registration time of
one resolution element by the radiometer AVHRR is 0.25 ms. Contemporary
IR-radiometry derives success in improvements from creating photoelectric
receivers with high spectral sensitivity (in spectral ranges 8–14 mm) Photoresistors
and photodiodes on the base of HgColTe are in considerably use. The maximum of
their spectral sensitivity is at 10 mm and the time constant ranges within 50–500 ns
with receiver cooling till 77 К. The significant advance of photoelectric receivers is
the possibility organizing photocells to lines and matrixes that allows avoiding
complicated optics-mechanics scanning systems in radiometers. New receivers call
putting new technologic problems for creators of satellite instruments: special
microcryogenic systems for receivers cooling with small mass and low energy
consumption; the necessity of fabricating receivers similar over their parameters
(that is important for multi-element receivers).
Improving the methodology of multichannel observations (elucidating the optimal spectral intervals and their number) increase the remote observations as well.
Nowadays there are not principal difficulties in creating multichannel radiometers.
A different situation arises with perspective constructions (heterodyne radiometers,
IR-spectrometers) that can provide the qualitative leap in accuracy improvement of
radiometers. The stable and highly coherent radiation sources are needed for
creating and using heterodyne radiometers that call cryogen system for satellite
IR-spectrometers.
Graduation of satellite radiometers is of most important stage in the instrument
preparation because it defines the results accuracy of meteorological parameters
measurements. It is clear that graduation of satellite instruments is to be accomplished in similar to operational conditions at satellite board.
However, the extended and careful graduating preliminary program of the
instrument is not enough for necessary accuracy of radiometric observation. In
particular 1–2 months are needed after instrument launching at the MS board for
stable running radiometer in operating regime ratings. For example, the radiometer
HCMR regime ratings characterized by the receiver temperature 150 К, but first
70 days after launching the temperature exceeds 200 К and decreases to 0.14 К per
day during 30–50 days.
The orbital calibration is accomplished during all period of instrument’s operation that regulates by following factors:
– “ageing” electronics that leads variations of the instrument sensitivity;
– changing conditions of solar heating the satellite and instrument;
– Possibility of ice deposition at cooled instrument elements because of degassing
and condensing processes.
Thus satellite radiometers demand continuous orbital calibrating during operational cycle at MS board for expeditious correction of graduating characteristics.
From the experience the orbital calibration is accomplished with both the reference
radiation of the space and boarding imitating of the blackbody. The absolute
calibration only with the blackbody is not sufficient.
6.1 Concise Theory
55
high space resolution. It is mentioned for comparison that the registration time of
one resolution element by the radiometer AVHRR is 0.25 ms. Contemporary
IR-radiometry derives success in improvements from creating photoelectric
receivers with high spectral sensitivity (in spectral ranges 8–14 mm) Photoresistors
and photodiodes on the base of HgColTe are in considerably use. The maximum of
their spectral sensitivity is at 10 mm and the time constant ranges within 50–500 ns
with receiver cooling till 77 К. The significant advance of photoelectric receivers is
the possibility organizing photocells to lines and matrixes that allows avoiding
complicated optics-mechanics scanning systems in radiometers. New receivers call
putting new technologic problems for creators of satellite instruments: special
microcryogenic systems for receivers cooling with small mass and low energy
consumption; the necessity of fabricating receivers similar over their parameters
(that is important for multi-element receivers).
Improving the methodology of multichannel observations (elucidating the optimal spectral intervals and their number) increase the remote observations as well.
Nowadays there are not principal difficulties in creating multichannel radiometers.
A different situation arises with perspective constructions (heterodyne radiometers,
IR-spectrometers) that can provide the qualitative leap in accuracy improvement of
radiometers. The stable and highly coherent radiation sources are needed for
creating and using heterodyne radiometers that call cryogen system for satellite
IR-spectrometers.
Graduation of satellite radiometers is of most important stage in the instrument
preparation because it defines the results accuracy of meteorological parameters
measurements. It is clear that graduation of satellite instruments is to be accomplished in similar to operational conditions at satellite board.
However, the extended and careful graduating preliminary program of the
instrument is not enough for necessary accuracy of radiometric observation. In
particular 1–2 months are needed after instrument launching at the MS board for
stable running radiometer in operating regime ratings. For example, the radiometer
HCMR regime ratings characterized by the receiver temperature 150 К, but first
70 days after launching the temperature exceeds 200 К and decreases to 0.14 К per
day during 30–50 days.
The orbital calibration is accomplished during all period of instrument’s operation that regulates by following factors:
– “ageing” electronics that leads variations of the instrument sensitivity;
– changing conditions of solar heating the satellite and instrument;
– Possibility of ice deposition at cooled instrument elements because of degassing
and condensing processes.
Thus satellite radiometers demand continuous orbital calibrating during operational cycle at MS board for expeditious correction of graduating characteristics.
From the experience the orbital calibration is accomplished with both the reference
radiation of the space and boarding imitating of the blackbody. The absolute
calibration only with the blackbody is not sufficient.
6.1 Concise Theory
55