IEEE Geoscience and Remote Sensing Magazine - June 2015 - 20

18000

-28

16000

-29

14000

-30
-31
-32
-33

350

400

450

500

550

600

650

Horizontal Baseline [m]

NESZ [dB]

-27

12000
10000
8000
6000
4000
2000

Ground Range [km]

0
0

-28

80 100 120 140 160 180
Time [Days]

Vertical Wavenumber [rad/m]

-32

0.64

-34
-36

0.56

0.48

-38
-40
350

400

450

500

550

600

650

Ground Range [km]

Latitude [deg]

AASR [dB]

-30

0.40
0.32

0.24
0.16
-50

0.18

RASR [dB]

-30

0.08
0

-35
-40
-45
350

400

450

500

550

600

650

Ground Range [km]
Figure 13. Noise equivalent sigma zero (NESZ), azimuth ambi-

guity-to-signal ratio (AASR) and range ambiguity-to-signal ratio
(RASR) for the B1/B2 imaging modes (cf. Table 2) of Tandem-L.
2) The data volume that can be transferred to ground in a
given time period (typically expressed in terms of daily down-link capability). Under full exploitation of its
multiple receive channels, Tandem-L can produce data
at rates that exceed the feasible down-link capacity in
the foreseeable future.
As discussed in Section III, the temporal evolution of
the vertical wavenumber is achieved by slightly varying
the inclination of one of the spacecraft. Rather than a linear variation of the baseline, the retrieval of forest structure
requires a given combination of smaller and larger values
k z . To achieve the required profile, a bistatic phase would
start with a small delta-inclination ( Ti ), resulting in a slow
growth of the horizontal baseline at the Equator, which
would be accelerated by successive increases of Ti during
20

60 80 100 120 140 160
Time [Days]

0.00

Figure 14. Left: evolution of horizontal separation (baseline) at
equator during a bistatic cycle. Right: vertical wavenumber as function of time and latitude for ascending tracks (incidence angle: 36°).

a bistatic phase. This is illustrated in the left panel of Figure 14, which shows the evolution of the Equatorial horizontal separation during a 176-day bistatic cycle. The right
panel in the figure shows the resulting vertical wavenumber
as a function of time and latitude and for ascending passes.
The North-South asymmetry is caused, mainly, by the rightlooking geometry. It should be noted that the proposed
mechanism to control the baseline evolution, fails to provide adequate vertical wavenumbers at very high latitudes,
for which a complementary approach may be needed.
The primary way to limit the data volume is by carefully analyzing the observation requirements and translating
them into the minimum mode (in terms of data rate) needed
to meet them. Once this is done, an observation scenario has
to be crafted that fulfills the scientific requirements while
addressing potential conflicts between applications and
considering the mission constraints. Since forest structure
acquisitions are tied to the occurrence of particular vertical
wavenumbers at the latitudes of interest, they have to be inserted first in the timeline. Forest acquisitions require 3 to
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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2015