The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Voi XXXVII. Part BI. Beijing 2008 
InSAR is operated in a so-called ping-pong mode which 
effectively doubles the value of the geometric baseline B. These 
equations become the basis for sensitivity and error analysis 
(e.g. Rodriguez and Martin, 1992). For single-pass InSAR 
airborne systems as described in this work, the signals are 
received almost simultaneously so that errors induced by 
temporal-decorrelation are not a factor as is the case for satellite 
systems such as ERS and Radarsat which operate in a repeat- 
pass mode. Provided the baseline length, position (from DGPS) 
and attitude (from coupled GPS/inertial) are adequately 
controlled and/or measured, the dominant noise-like error 
source arising out of these sensitivity equations is ‘phase noise 
o<p so that the signal-to-noise ratio, which is a function of 
flying height among other system-related factors, becomes a 
means of (partly) controlling height error specifications. That is, 
other parameters being fixed, the height noise will increase as a 
function of flying height. For example, DEMs created from the 
STAR-3/' system, when operated at about 9km altitude, has a 
height-noise level of about 0.5 m (1 sigma, 5 m sample spacing) 
at the far edge of the swath. Systematic errors, with reference to 
STAR-3/' DEMs, are usually slowly-varying and arise from a 
variety of sources but are limited through calibration, 
operational and processing procedures 
Figure 1. Schematic of Airborne IFSAR Geometry. 
2.2 Current Intermap Airborne InSAR Systems 
In order to meet the schedule requirements of its NEXTMap® 
program (Section 3) and other demands, Intermap has recently 
developed three additional operational airborne InSAR systems 
(Figure 2) to supplement the acquisition capability of the 
STAR-3/'® system. STAR-3/', is an X-band, HH polarization 
InSAR flown on a Learjet 36 (Tennant and Coyne, 1999). In the 
last few years, all of the software and most of the hardware has 
been replaced in order to improve product quality and 
efficiency of operation. The new systems are based on a 
common architecture and are flown in 2 King Air and 1 Lear Jet 
platforms respectively. The systems are described in somewhat 
greater detail in Chapter 6 of (Maune, 2007). The addition of 
these systems has greatly improved scheduling flexibility and 
capacity. 
2.3 Product Specifications 
The core InSAR products available from Intermap’s online 
store include an Ortho-rectified Radar Image (ORI), a Digital 
Surface Model (DSM) and the bare earth Digital Terrain Model 
(DTM). X-band images are at 1.25-m resolution with similar 
horizontal accuracy. DSM and DTM are posted at 5m spacing. 
The elevation products are available in three standard vertical 
accuracy specifications as illustrated in Table 1 below. It is 
worth noting that all four of the STAR family of sensors are 
able to achieve these product specifications despite the nuance 
of individual system design or platform specifics. Apart from 
these core specifications, other accuracies and image/DEM 
resolutions can be supported to meet specific requirements. 
Optical/radar merged products are now also becoming available 
as exemplified in Section 3. 
Figure 2. Clockwise from upper left: STAR-3/', STAR-4, 
STAR-6 and STAR-5. 
Product 
Type 
DSM 
DTM 
RMSE 
Spacing 
RMSE 
Spacing 
I 
0.5 
5 
0.5 
5 
II 
1 
5 
1 
5 
III 
3 
10 
- 
- 
Table 1. Intermap Core Product specifications for InSAR 
DSMs and DTMs. All units are meters. RMSE refers to vertical 
accuracy and is with respect to terrain that is moderately sloped, 
bare (DSM) and unobstructed. DTM specifications apply to 
areas for which the forest or other above ground cover is 
‘patchy’ to a maximum scale of about 100 meters. Details of 
these specifications may be found at www.intermap.com. 
2.4 Operational Components 
The operational flow consists of four major stages: (1) planning 
and acquisition, (2) interferometric processing, (3) editing and 
finishing, and (4) Independent Quality Control, after which the 
data are delivered to the data base repository. The operational 
concept has evolved to accommodate the requirements imposed 
by the current NEXTMap* goals as well as custom projects. 
The NEXTMap® Europe and USA objectives alone require the 
data acquisition for an area incorporating 10.2 million km 2 by 
the end of 2008. All aspects of production are managed with 
rigorous QC checks throughout and within the framework of 
IS09000 certification. 
3. NATIONAL MAPPING PROGRAMS: NEXTMAP 
NEXTMap® is the term used by Intermap to describe its 
InSAR-based national and regional mapping programs. 
Specifically the concept is to make DSM, DTM and ORI 
products generally available in a seamless fashion over national 
and trans-national regions where multiple applications and 
markets may benefit. By retaining ownership and licensing the 
data to multiple users, the cost is shared, making it feasible for 
public and private organizations to have access to these data